HP BEEP CODES or Keyboard LED BLINK Codes.                            

This really IS BIOS P.O.S.T ERRORS , as it discovered bad thing (serious too) at the lowest levels of software called BIOS.(mostly hardware errors found)
POST means , power on self test. 

There are vast codes  possible even more with a POST CARD  . (read your service manual yet?)
Today we have only BLINK codes. (keyboard blinks)
All codes are BIOS related.  (generated by it)
Not only that, but there are and were many different BIOS makers even Pheonix BIOS had them in 1979 and newer.  (HP 1984 to now)
Be wise for all PC owners to enter BIOS setup and see what is there (name of maker and version #)

There is this PCI circuit card (POST CARD) you can buy, that gains access to even more BIOS error codes. (this can work or not, depends on the BIOS makers rules) See sellers store here. (see photo end of this page)

Hp.com has your PC listed (if not too old , over 10 year last one made is the limit)  and the guide pages there, show the Service books and they tell you all codes for your exact MOBO (mother board)

HP has this page on BLINK codes et cetera , covering  newer PC's. Before and after 2010.

The old codes are the most hard to dredge up.... See old Pheonix V4 book here. page 39(pdf page)
On super old PC , BIOS V4 one beep means I'M OK. "One short beep before boot" this means booting NOW.
Even overheat codes from users not cleaning there PC's of lint , tops the all time #1 cause of beeps.  CPU overheat codes ! All PC like cars, need service, and cleaning or will fail.

The Pheonix BIOS ,seen in the above links, has the most codes of all. 50 codes or more !  SHOCKING NO? But may only beep 10 ways. 
Some newer but not NEW BIOS has like 4 or 5 beep codes,  No ram, bad Ram, missing VGA card, CPU bad , CPU overheated.
AMI BIOS had 8 codes.
Award 6 BIOS does a long beep and then sends messages to the screen.

Most PC 10 years or newre all do BLINK codes now.
Blink codes, is the  better name as the chip uses FLASH memory so can be confusing, if you call them flashes.
Amazing HP has a page just for this too.
The beep codes became, and moved to the NUM/CAPS lock keys LED lamps Blinking codes.  (silence is golden?)

Common errors:
  • BIOS ROM checksum  (or the time-o-day clock fails) the COIL CELL BATTERY IS DEAD,  after 5 years, they do that. (1-2-2-3 beeps)
  • Even a stuck keyboard key can cause errors here.  (remove the keyboard, did the error clear?)
  • Also bad RAM, or using the wrong RAM chips here ,will cause this, or all RAM missing. (try each stick only 1 by 1?)
  • CPU overheat, (never cleaning fan and heat sink fins of lent?, is a sure fire way to get this error, or the CPU heat sink fell off, or it's fan dead) {and other ways}
  • VGA (graphic GPU) card errors, or bad. (try another is only solution here)
  • Hard drive fails to boot errors. (hard drive bad, cable fell off, and more)
  • If you remove something and  the error changes, changes to something else,  like missing Keyboard or missing a factory VGA card or RAM missing.
  • There are many more,  possible,  only the book on your exact PC and BIOS covers what is possible and cures.

I do not have COMPAQ blink codes or beeps, for system this old , Google is your only possible way to find facts on these very old laptops. 

Here is my HP8540W Laptop, with many parts missing,  even with NO CPU the power control chip can still tell you (strange blinking) that it is missing.

MP4 9-Second video demo, no CPU

OGG 9-Second demo , no CPU (Firefox likes this)

What the H3LL is beeping, this ! it is called a Piezoelectric sonic beeper,  Replacing the COIN cell is  GOOD MOVE !

How A POST CARD looks, LIVE  ,as you boot , the card rattles through a bunch of numbers (tests)  and if all is ok ,it lands on 7F hex. (binary 0111,1111)
 If not, then it lands on an error and hangs. Telling you the error code. This is  a PCI slot below. Your BIOS maker will tell you what this code means.

version 1.  6-4-2017