Panic ! or Not
 I want to Backup my data now or recover it. (for any reasons whatsoever)
And all ways to prevent this in the future.
( If the HDD is   sick , we might get Linux to recover files

You have no cloud backup so...
One wise thing is never store data on your BOOT drive, then when windows goes corrupted the data is not lost.
If you run any kind  of backup application  or even try to drag and drop files , a bad HDD will cause huge blocking progress  errors.
There are vast ways to backup and depends on if your HDD is good or sick.
Sick means S.M.A.R.T test on the HDD failed. (HDD have 3 states,  Good, Bad or SICK, sick means the autorepair engine RAN DRY)
If the HDD is silent, or can not be heard to spin, all hope is gone if power plug did not fall off? ,so stop and break out the crying towel. A 5 year old drive can fail; for a fact.
I use  EaseUS  TODO backup V11+ (to external file backup servers and to other media)
If lucky Linux can find it in a pinch and you can backup/ recover files now. 
(Using the Demo mode, "try me" and run HDD tests first)
If the HDD is sick only forensic recovery applications can work.
There are endless tools, that can un-delete files.
(Google that, it is covered a zillion times , all the way back to good old Peter Norton era 1980s))
Files that are corrupted, sometimes can be repaired in whole or in part.
(complex endless topic here, ask a professional for help; get help or see forensic tools above)
A hdd can not be repaired,when the internal HDD repair engine dies , that is it. (if the bad clusters can not be logically replaced that is the END)

Backups need not be hard, ever.
A young student might only backup to 1 or 2 thumb drives (udisk, usb stick memory) (no big cost there)
He or She would save each time using a new file name,  like this,  my_project1,docx  , my project1b.docx.
That way you can get to older versions if you have one go corrupted.
The top reason to USB corrupting is not right clicking the USB task bar, icon and clicking "Eject mass storage"
And not using 2 USB sticks and using them in alernate fashion, (never trust one stick , ok?)
If you were say an  engineering student, all this is old hat, you have your own servers at home, and at the school and have a paid for server say here. (even an FTP storage there , like me) Or there cloud.

Do not use this method, ok:? Unless highly motivated ! (tongue firmly planted in my cheek!)
Funny joke here!, but there are great $2000 high end tape systems still used.
Backup to any thing you want, USB stick, HDD #1,2,3, etc,
External HDD (USB inclosed HDD or SSD) is best.
Backup on your home network to spouses PC, with 1 shared folder. (now you have it 2 places)
Back up using DVD-R or BluRay disk BD-R using ImgBurn.exe free program.
Backup any cloud you want.

 I will not even mention XP or VISTA as both are dead now, 100% dead. (per wiki world wide, usage clock) Dead and gone RIP for ever those.

Frequency of backups:
There are 2 kinds of users, (really lots more but..) 1: backs up every day , or 2: never !  ( a wise Student or Business professional has 2 backups every day)  One, say on a server and one on a USB memory stick.
Backup as often,as you can afford to lose data, for gamers it's not too important unless game progress is Okay to loose.
end backup rants...
Example below is of a HP Laptop, Mfg. date: circa 2010 ,

THE BELOW IS FULL OF EXAMPLES of no 2nd backup and most try to get to data lost on say your C: drive. The boot drive, has gone WONKY.

Hint 1: if running windows 7 to 10 and lost your CLOUD password , See how to fix it.
Any other lost PW or dead OS or dead HDD, it is now time to backup data,  before , installing any new OS.
We first try to get the data, many ways and then back it up pronto.  (there is program called recover-it Pro $40, that can even get data off a deleted partition)

Way 1:
The Virus  killed your only log-in to say Windows 7,8,10.  (there is never limits on what bad a Virus can do... not really) AS CAN A BAD Hard DISK (HDD)! (we are recovering a Local account here)
The savvy owner has a 2nd or 3rd account on the PC as Administrator, or Windows will not let you access other accounts. (  Say from Admin to Say Larry's account) (the guest account is useless here)
Bam   on, this PC, it  has no Admin account or is corrupted or the owner has only  guest account and the default off line admin was never activated.  (as is usually the case)
The owner now wants to backup his/her data (I will now use the word his/him to mean his/her from now on , dig?)

My HP has the MAGIC  F11 key that takes me to the "HP Recovery manager",  I click backup and the manager tells me I can backup, but if this works you are home free to , fresh Install HP Windows, with F11 the 2nd time.
HP offers 2 choices, Backup or Fresh Install (kills all data). (unlike Windows OEM K choice, install and kill data)  (a 3rd choice is buy a Windows Retail disk W10 and do an upgrade now, (keeps data/apps)
Way 2:
The owner (or tech)  now boots to Windows Live PE 10,  (off stick CD/DVD are now dead meat)  {built using Rufus app} The Stick boots,  on my HP gear hit F9 (HP forced boot mode ,love it)
I boot to PE,  and my disk is chock full of apps.
I then try to access my data, found in C:\users\username\   {  replace username with your account name seen there, that you want to retrieve} (my documents, tops the list , in there)
Warning windows is now mutated to extreme, security now (w7 is even patched (updates) to be more like w10 now) So do not be surprised that any Windows PE disk , will block you from files that are yours.
One time I tried  (2017) the PE told me , to give owners PW, and I did that, but the Virus had killed the PW code some how.  (dead log in) Yup, worst case can be dicey....
If you have and Admin (true) login on that system,  you can get all files if not corrupted. (directly and the most easy) Always have  Admin account, activate the hidden one.(use it only for emergencies like this)
Lets say this fails.  What then.?
Way2: may fail (permissions blocks), so you remove your offending HDD and connect it to any other PC as drive 2,  and get your data. from your Users account above. (if it lets you)
Best way now (2017) is to avoid windows totally. (the above ways, do  work on older OS !)

Way3: (in all cases here , the HDD spins ok, and some data is there)
Next is Linux.  (you have no other choice now, Windows failed you "my point of view")
Linux cares not beans about Windows strict file security rules, to Linux it's just data files, so long as no partition corruption or NTFS structures are damaged, I will cover that last (that is worst,worst case)

I take my Rufus APP v2.13. Portable version , I like, and build a USB stick from ISO,  best ISO is the HUGE one 4Gb, called the full DVD version.V7.6 EN is what I have. (or newer, newer is always better in Linux world)
 (the 5 USA links are dead, so here is England Servers, but get the ones ending in EN.ISO for English not DE for German )

Rufus is easy to use, Google how to use it. (one can also burn a DVD with free imgburn.exe (google it), get them from the real makers site, never use download-virus-site-dot-com.
Linux is not too scary now, with Windows drive automounts, etc.  Desktop and file explores, (many).  IMO
The newest Linux is best, so it can operate newer PC chips , wifi , wired and mount USB drives instantly.   Here  I am doing this step.,..
 1,2,3 steps is all it is. (my stick is in D: make sure you get this correct. "look, then leap" )
If your PC can boot a stick this works for sure. (if not, use a DVD disk Linux live boot.)  I can also boot to Unbuntu v16+ in demo mode ("Try Me") and find file this way.

We now boot that stick and retriever all my USER/username ,data and put said data on any external media. (external means not your failing HDD)  SEE EXAMPLE HERE.

Last, is what we call computer forensics today,  (old name, data recovery)  (forensics goes way deeper...and can be overkill, but is a choice)
There are some real great and expensive software, sold to get data from corrupted places or deleted files. (Google finds them and let your pocket book tell you what to do? I can't) {and endless changing topic if ever there was}

Here are some free choices, read how to use them by clicking the links.
The first one can repair corrupted structures.
The next one,  can give you access to all data,where possible. (some software can find the , impossible, but not if the sectors were over written say after you deleted a file)
I'm using open links 2 below, so you  can see you are leaving my site.

Be aware, that  some Software (Forensic) can even recover part of a document.  (say a 300 page thesis and gets 290 pages?) Or  all of a deleted file.
Learn to use  your PC more wisely, each day you edit some huge document or work, save it each day with a name (number)  , lets say its a huge PDF,
Day1,  save as (mystory1.pdf) then day2, save it as (mystory2.pdf).
Then at the end of the week you have 7 files or in a month 28-31 files, then later if you are doing a recovery, you never loose more than one days work.
On old main frame computers this happened automatically, like a DEC, VAX(VMS OS)
Sure, every day backup to other media, cloud or server.  (best is to backup off site, so if the PC is lost/stolen or say lightning blew it to kingdom come, you still have every days work, every single one?

Here is my wish to you ,that your DATA is easy to  find, and super easy to backup.

My PCs all have 2nd SSD, (hdd) so I can backup to the second drive at any time, and to a stick my data.  (my laptop the optical drive is removed and has  SSD caddy there now)
This gives me backups in 3 places,  C:  , D: and STICK, (all 3 can never crash at once, but could be stolen,  for a cure for that, is put your data in your off site server or Cloud)

My last hint , always have an External HDD drive,(SSD) that is eSata ready so you can back up and then turn it off.
I have 3 backups. (besides my PC's C: drive)  (this adds up to 4)
Blu-ray BD-R (CD-R is ok so is DVD-R) (can be USB external drive used for backups)
External HDD (2TB or more) eStata best, USB 2nd best.
and a USB STICK (the really paranoid use rotating USB , my friend uses 7 USB sticks, marked Monday to Sunday, for the reason , why trust just 1?) once bitten 10 times shy?. (in the world of creativity)

Good LUCK !  "My the force be with you"

The early bird gets the worm, but the 2nd mouse gets the cheese. (be backed up and win !)

Examples (Knoppix)  See the cheat sheet,  HERE: I use this "knoppix no3d" at boot.          (RTF HERE)
Ubuntu Linux is my favorite, but the below, works very very well. I even tested this on a Windows 10 HDD.
Knoppix running, now... drag files you find to other media, I personally like to my server or to my USB attached, HDD. 2TB.
The files are all completely accessible ,copy any thing you want to anywhere, for sure that /users/ folder.
Keep in mind ONLY you know where your data  resides, that is what folders what drive, what partition, etc., but if you only need JPG or DOC files just do a search for those.
We can also make Windows 7 or 10 PE boot DVD or STICK (usb) and find file that way, if your OS is dead or infected. (google that and how)

Version 3.  4-8-2017  By Deadpool.   ,revised 11/2018