Very odd NO POST problem

[Zairex]

I have my own custom-built computer. It has been running smoothly for little over half a year.
FIRST: When the computer is off and I press the power button it does one of four things:
1. Begins booting up and immediately restarts.
2. Begins booting up but there is no POST (no video, no USB power, etc.)
3. Begins booting up, POSTs, then freezes
4. Actually boots correctly

The most frequent outcome is #2. when I leave the computer off for more then 30 seconds and try to restart #1 leads to #2. #3 happens almost as often as #4 (Over 75 restart attempts, it has only POSTed twice)

SECONDLY If I let my computer go into sleep mode, there is a 50 / 50 chance that it will not wake up again and I have to restart.

Does anyone see an obvious diagnosis that I am missing? I really need to get it working.

Here are my components, if needed:
CPU: Intel Core2 Quad Q9550
MoBo: ASUS P5Q Pro Turbo
RAM: OCZ Gold (3 x 2GB) DDR2 800
PS: OCZ 500W ATX12V V2.2
OD: Samsung 22x DVD+/-R
HDD: HITACHI 1TB 7200 RPM Sata
VC: Sapphire Radeon HD 4870 1GB
OS: Windows Vista 64-Bit

 

[Tmagic650]

This may be caused by a failing or corrupted hard drive

 

[XOR]

I've had this issue before on my P5Q-E the system would go into a endless reboot cycle, or it would start booting then crash.
Asus has a feature "ASUS C.P.R.(CPU Parameter Recall)" that tries to reset the BIOS after a failed overclock/setting change or even a failed boot. This works most of the time but sometimes the only way ill get my system to POST is by removing the RTC jumper and resetting the BIOs. (Of course I'm trying to run my Q6600 at 4.0ghz on air, not gonna happen)

If that doesn't work try the suggestions below
Un-plug all your hard drives/Optical drives/Keyboard/mouse, and all but stick of RAM. Now see if it POSTS, if it does start adding all the stuff you un-plugged/took out until the machine doesn't post anymore then you've found your problem device.

If it stops POSTing when you add all your RAM back in you have a RAM issue.

Now if the machine still refuses to POST with nothing but the bare minimum I'd say you have a PSU issue.

Your 4870 has 4 LED's on the back of the PCB, 3 of these should come on for about a second once you power on your computer and then turn off, if one of them stays lit you have a power issue the exact LED meaning can be found here 3 have to deal with power to the card and one has to do with temp.

Hope this helps.
PS: Sorry for the poor spelling and grammar

 

[sllewe]

I do not think it is a hard drive issue, as it should POST even if the HD is dead/dying.

I would follow the instructions posted in the post above, my guess something is wrong with the RAM or low level chipset.

Even thought the quality of capicators is much higher then it was in years past, it wouldn't be a bad idea to take a visual inspection of the capacitors on the board for any that are bulging/leaking