HOW to do a PC HARD RESET           
  A dead PC ?, many only need this to cure the dead.  (a goal here is to get the PCs fans spinning and BIOS screens working with only  RESET)

Every OEM PC maker in the business online has these simple instructions in there MANUAL (steps 1-4), (for all PCs made, for sure all Desktops and Laptop, I do not cover Notepads, ask your OEM for help) 
Even simply holding the power button in for 5 seconds and then releasing it, can reset most PCs. 
  • There are 2 reasons to do these steps , the PC is dead, and needs a reset for sure after ESD or near lightening events or AC line power surges. (causes logic LATCH-UP) or resets the  silly sleep modes.
  • Or you want to work inside any PC, at step1 cover off and hands about to touch things inside (stop your self and think) (avoiding hot swap damage caused $$$ by you)
  • Remove all USB devices first and hold the power button for 5 to 10 seconds and release, does the PC turn on now?

RESETTING ANY PC:
This  is mostly a motherboard reset or is done only to make the system safe (step 5 ) to remove parts (RAM/PSU/PCI/HDD/SSD) or get the PSU ready to bench test.) 
This cures PC's stuck in sleep mode  or  with any chip (I.C)  CMOS latchup or ESD / lightening event lockups, steps 1 to 5)
If sleep mode is stuck this is only temporary fix, because your PC has bad/wrong or corrupted DRIVERS.  (software drivers) YOUR OEM has the cure, ask them now. (or turn off sleep modes)

If the RTC coin cell battery is dead, replace it below 2.9vdc is bad. (if this tiny battery goes dead,  the BIOS and NVRAM  goes nuts as "Robot CASE says nothing good can happen. (a hopeless place to be for a $1 part)
If a Laptop of any kind, portable PC of any kind the main battery must be removed or unplugged first. ! (and only put back later only after proven to be good. Shorted or near shorted batteries can cause rail overloads. (and chaos)
  1. Make sure the optional PSU rear  rocker power switch is in the "0" OFF position.  IF NOT make it so...
  2. Remove the Thick A.C. Line cord (cable) from the wall Outlet at either end  or both ends. (this is the best way)for sure lacking rocker above !
  3. Push the front power button for 3-10 seconds. ( the fans in the PSU may spin for 1 second and die, this action heard/seen,  are the  Capacitors fully discharging)
  4. Release the  power button now. I also repeat #3 until I see the fans stop twitching (yah get all the CAP.'s fully discharged is the #1 GOAL here)  
  5. Wait 5 minutes, touch nothing. (this waiting can help you discharge the Cap'.s deeper) (and is optional and advised)   { a level 1 reset
  6. At this point you can work on the PC inside and not damage parts removed or installed hot swapping them.
  7. If  only doing the hard power reset then  reverse steps 1 to 4 and PC now it runs and works perfectly (but may fail again soon if the PCs software drivers are bad and sleep locks up again) Sleep mode can lockup, and is common.
  8. If only doing internal service to the PC you are now safe to work at step5 (no damage to the PC now) do not HOT SWAP parts in any PC. (inside parts, ALL)

If the PC still  fails?, remove the RTC Coin cell, and repeat  step 1 to 5, then put it back and reverse your steps.  (I call this a level 2 reset)  { a new or tested COIN cell now is best}
Any time a coin cells is removed, you need to do one more step, go into BIOS (DELL F2, HP ,esc)  and do BIOS reset to defaults, (then turn PXE off in BIOS if present)

NEXT A LEVEL 3 RESET:
If at wits end?, (been there many times)  is to pull the coin cell and do steps, 1 to 4 with coin out and then wait 1 to 4 hours, and put the coin cell back on and AC back, and power the beast up.
or wait over night like this, with no AC power cord and no COIN cell present in PC. (Laptops?, the HUGE battery removed first, or unplugged as the case my be...) Then put all that back together and power on the PC.

Some PCs have huge amounts of capacitors inside, in PSU, MOBO, HDD, DVD , Huge video cards with banks of caps that do NOT WANT TO discharge to 0 volts DC easy.  
 

Last is a Level 4 reset . ( 99.9% not needed ) If the over-night trick fails.(above)  (  this if you just planned to buy a new MOBO, so don't do that yet do the below)
RESET extreme, is level 4,  I remove  all parts connnected  the MOBO,  all RAM, CPU, all cables,USB devices and PSU cables, cards too. (step1 to 4 done above first)  (100 % total dismantling)
Make sure to re-seat the power button cable to the Desktop mobo port, keep this here at all times, on some laptops the power button is just 100% bad, replace it if suspected.

 #4 method , is for very stubborn Cap.'s in the PC that fail to discharge fully, then I leave  it like this for 1 full day, all naked and no power sources of any kind and the COIN cell out.
I the build the PC back using the stripdown steps the same.

WHY latchup happens (DO NOT READ THIS, IT IS PURE TECH)  (all it takes is a power surge for  this to happen)
Last and on topic, I wear a ESD wrist ground strap to work on all PC internals. (<this link shows the huge damaging levels of ESD possible)
(or keep your other hand holding metal ground in the case)
Latchup CMOS SCR Parasitic caused.

Latch up happens, for many reasons ESD electro static zapping any PC ports, or devices connected to any PC.  (ESD= elecrostaic discharge)
Lightening hits, 
near by your home,  direct hits are catastrophic.
Hot swapping parts inside any PC. (stop doing that )
Power surges of any kind, even AC line overvoltages or other causes.( AC power company caused , most times)

To a PC user (personal computer) the top ways to prevent latchup are:
  • Buy Newer PCs and that gains you newer better advanced CMOS logic chips, and better protective devices inside.
  • Do not hot swap any thing inside any PC, USB is ok outside as are  Video ports outside, but never INSIDE.
  • Do not handle parts inside any PC and not using an ESD strap while working, or just keep one hand grounded to the metal frames inside.
  • Use a UPS for the AC line power to a Desktop PC,  Line voltages (AC) can have huge surges and invites LATCHUP.
  • Unplug expensive equipment , like your PC and TV to prevent lightening hits if the weather turns south (bad) or a UPS power supply.
The actual voltage to release a latchup is not exact,  but is when you hit this corner here, (red arrrow) the latching event ends (Cap.'s finally discharged to this point and the PC now wakes up from a latched up state)

I covered every possible way to reset  a PC, (hardware, not software) Most times just holding in the power button for 5 secondes, is cure or unlocks the faulty sleep modes in most PCs

What happens if I hot-swap, things inside a  PC, "Nothing GOOD!"

A PC is not 100% off, until the power cord is removed from the wall AC power jack.  (all PC have hot standby power at all times)

version 2.  12-9-2017 (revised 9-1-2019)