Hi all, I'm new to the board (although I use TH for all my hard ware needs!)

I'm at my wit's end with a PC that I built about 4 months ago. Here's the hardware list:
CPU: Intel Core 2 Duo E6600
RAM: 2x1GB Crucial Ballistix PC2 8500 (replaced under warranty)
MOBO: GigaByte P35C-DS3R (replaced under warranty)
GFX: XFX 8800GTS XXX
Case: Antec P182
PSU: Hiper 580W - replaced with Zalman 600W

The problems first started from the beginning when Vista kept giving BSoD. I put this down to Vista being pants, so went back to WinXP64. Problem persisted so I RMA'd the MOBO and RAM. Problem went away for a while.

Last night, I switched the PC on, Windows froze at the loading screen. I powered it down, then up again. The PC has since then gone into an endless power cycle loop, where it powers up (fans come on, HD's spin up), 2 seconds pass, powers down. I have unplugged everything bar the CPU and it makes no difference. The only thing I have discovered is that when I unplug the separate 12V rail, the whole thing powers up, but nothing happens. No POST, nothing on screen. To add insult to injury, the P182 doesn't have a built in speaker - so I can't get any beep codes (and I don't have any spare ones knocking about)!

So I was wondering if you guys might know what this power cycle loop is. Is the CPU dead?

Thanks in advance!

Unzip & burn it on cd/dvd as image & boot it up:

http://www.memtest.org/download/1. [...] 70.iso.zip

Wait for 5+ passes. If no errors, your components are good. It's probably software - windows.

Ok, I missed the last part. Your pc won't power on normal. Did you update bios lately or a program set to do so auto? If so, clear cmos.

By separate 12V rail, you mean the 20-24pin of the atx mobo power cable? Or the 4-pin cpu power?

You can buy a 15$ PCI card tester that will read the HEX output of the mobo and tell you where the computer is failing. CompUSA sells them.

00/FF are failed mobo/CPU, but with the error code, you will know more. System does not need to boot to a display to read the hex, it is displayed on the card.\

Also, can you boot into another OS (linux), or the BIOS without issues, while the 12v 4pin is connected?

Try powering up with just one stick of ram. If it can post, go in the bios, and make sure the memory voltage is 2.2v.

I saw on new egg the spec's:

Crucial Ballistix 2GB (2 x 1GB) 240-Pin DDR2 SDRAM DDR2 1066 (PC2 8500) Dual Channel Kit Desktop Memory

Hope that helps.

Edit:

another thought, look through your manual, and make sure your MB can handle that speed. I saw/read that some MB act goofy when running it at default. You may need to bring it down to DDR2 800 speeds or something to that effect.

If you can, try testing the CPU in someone else's computer. If it fails there, then the CPU is bad. If it works, then its not the problem. Do the same with the ram. As Grimmy wrote, also try one stick of ram at a time.

Anothor possiblity is a bad PSU. I notice you replaced the Hyper 580wt with a Zalman 600wt. Any particular reason? Anyway, a faulty PSU can cause the computer to go into an endless loop. The computer starts to power up, fails, and then tries again, fails, etc. A common cause of this is a bad resistor which starts to heat up and then breaks contact. Of course, it could be a bad resistor in the mobo as well.

Just a couple ideas.