Hp pro won't boot up .. black screen

[Ahmedsaadawey]

Hello,


The problem I've got with my HP desktop started few weeks ago. When I turn it on it powers up, fans are running, but screen remains black - goes to sleep or displays "check the signal" info, keyboard and mouse are not powered and HDD light on the front is off. The only thing that works is DVD drive - I can open and close it.
In the beginning it could be solved by turning it off from the power button on the front and starting again. But slowly it degraded to such point, where nothing works, except rare times that "magically" it gets power and starts.
This is working only if I shut it down from a power button in the front and immediately start it again - but as I said, it works SOMETIMES.
I've already run through the steps in documents:
http://support.hp.com/us-en/product/HP-Pavilion-p6500-Desktop-PC-series/4162263/model/4215698/docume...
https://support.hp.com/us-en/document/c05336130 (Link Updated 04/26/2017)
with no success.

So far I tried the following:


- I tested it with other screen and got same behavior.

- I tried with new screen cables - DVI and analog with adapter.

- I opened the case and cleaned everything (there was not much dust, but still...). I did it with everything unplugged and made sure to ground myself.

- Checked RAM - I've got 2 RAMs in my PC (original ones) - 2GB and 4GB, I tried swapping them, running with only one in different slots - no success. Starting PC without any of them produces the correct "beeps" from motherboard though.
- Disconnected everything and held power button for about 1minute to get rid of any static - no success.

- Reset CMOS and when it didn't solve the problem I replaced the battery on motherboard - problem persists.

- Replaced VGA with the new one. I also checked with integrated VGA, but nothing. Then I put back the original VGA as it needs less power than my new one and I thought it might be a PSU issue.
- Replaced PSU with brand new Corsair, more powerful than original 300W - same story.

- There is no visible damage on motherboard, none of capacitors is puffed up, no leaks - everything looks just perfect.

- After research I also tried to disconnect memory card reader, but it didn't solve the problem.



Also, after putting the new PSU in I had another problem, where not only none of the USB or screen would be powered, but also the light on the front panel would be off, despite PC running. This was solved by resetting CMOS again, but I'm back to original issue of PC not booting and not powering peripherals as well as HDD.

Finally yesterday it did start after several failures - I had to shut it down from power button in the front and start it immediately again about 10 times. Eventually I saw HDD light coming on and the peripherals getting powered. It did restore default BIOS settings and succesfully booted.
Funny thing is, when it manages to boot, then it runs with no problem - no restarts, no BSODs, no weird behavior, it's quiet and smooth as it should be. I did not turn my PC off since then, as I'm afraid it won't boot again, but I can't keep it running forever - it's not a solution to a problem.

[mdklassen]

You seem to have replaced everything except the motherboard, without solving your problem.

So, what happens if the "flaky/intermittent" motherboard is replaced?

Do you have a spare motherboard (or "bare-bones" computer), into which you can temporarily install your RAM, your disk-drive, either the old or new power-supply, and your USB keyboard & mouse? Do the lamps on the USB keyboard & mouse light up?

[TedMittelstaedt]

These are textbook symptoms of a system with bad capacitors.  I know you didn't see any puffed up ones but it is not always that they puff up when they fail.

S.O.P. in these cases is to swap power supplies and if the problem doesn't go away the bad cap is on the motherboard.

It's possible to replace every electrolytic capacitor on the motherboard and get it working again.  But I have done bad capacitor replacements on motherboards where I only replaced the visibly puffed up ones and I only got a 50% success rate out of doing that so I gave up on it years ago.  If you have more time than money it might be worth trying it but you will need to replace every one.

Back your system up and then scrap it.