PC Wont Post, No Video, No Beeps

[Supernatural]

• I understand this gets posted alot. I've done alot of research on the subject keeping that fact in concideration. No I have all the Problems that have been noted down. I've completed all the Fixes that have been posted in replies from various forums.
• I recently changed from 7600GT PCI-E Over to 8600GT PCI-E and returned it because it was somehow slower than my 7600GT.. -_- made no sense. But I put my 7600GT Back in perfectly, now I've built PC's for many people. Kind of made a small business out of it.
• I plug in my power cord to the Power Supply and it turns on before i even touch the Front panel power on button. So I figure maybe a short was in the PSU. so i got a new one.. same Problem.
• Later I Decided to check out my cousins PC as it is basically the same as mine. Put My CPU in his and the PSU Which had the watts and voltage to handle the Dual Core and now he has the same problem. I've mixed around all the hardware from both PC's and I've narrowed it down to either CPU or the Motherboard being shorted out significantly by the PSU. I tried on Both motherboards the CMOS resets, taken out The Video Cards, CPU's (which has been working fine before) PSU's which were all working fine RAM of Course because i understand that RAM can be a real pain with PC's not Booting. I get No Boot Up, Monitor is blank and I have no Beeps wat so ever. I checked the Motherboards for Burns, Bulging or leaking capacitors or any damage and found nothing. Is it Possible the PSU Could Short the Motherboard out to the point is wont boot? Here are My Specs
• CPU: AMD x2 Dual Core 4600+
• HDD: 320GB Sata HDD
• MotherBoard: Gigabyte K8NF-9 939
• RAM: 4GB Samsung DDR400 (1GB Sticks x4)
• Graphics: Gigabyte 7600GT PCI-E
• PSU: Cooler Master 550w RP-550-PCAR
• Even with the new PSU installed as soon as I plug in the Power Cord and switch it on at the back the PC Starts Up. But I get No Boot, Blank Screen and No Beeps at all.
• I've narrowed it down to The CPU or Motherboard. But If Anybody has had my problem and can narrow it down to an exact. Please Let me Know

[disophisis]

You said that when you plug the power into the psu it just automatically starts up?

did you try taking the PSU out and just plugging it in and seeing if it turned on while not giving any power to the mobo?

[Supernatural]

Ok Yep I tried plugging it in with no connection to the Motherboard and it wont automatically start up. Its kind of strange how both motherboards now do it one was perfect until i pulled it apart. is it possible for a PSU to damage a motherboard?

[disophisis]

it looks like it is quite possible and actually probable:

http://ezinearticles.com/?Motherboard---CPU-Damage-From-Power-Supply&id=478613

[Supernatural]

It was a really weird scenario. I work on PC's alot and i didnt want to believe it lol.. The Damage happened directly after I changed the Graphics Card Over It was working perfectly otherwise. Then I tried to start it and Nothing at all came up..

[disophisis]

I'm sorry for your bad fortunes... but it happens to the best of us.

I'm not sure exactly what parts have been affected, but most assuredly the power supply is junk.

The motherboard is probably not that well off either. You might have to do some testing with replacement parts or swapping parts around to figure out what exactly you need to replace.

[Supernatural]

Well I've Decided to Get AM2 Pin Mobo and CPU now Plus new RAM I've gotten a New Power Supply. I had an Antec (Which I assume Damaged the PC) and my New Coolermaster PSU that seems alot better. The Problem was I used the Antec PSU in My Cousins Computer and I think i may have damaged his motherboard or CPU also. so its really not good for me money wise lol :(

[Supernatural]

It Was Indeed the Motherboard that was the problem! :(