System Shuts Down after ~30 Seconds

[zylaxice]

This is my first build, based largely on advice I picked up on this forum, so I'm hoping someone will be able to help me resolve this issue.


Parts
EVGA NVIDIA nForce 780i Motherboard
Core 2 Duo E8500 Wolfdale @ 3.16Ghz (stock fan)
EVGA GeForce GTX 260 Core 216
OCZ GameXStream 700W PSU

Stuffed into an Antec 900, with a 640Gb Western Digital Caviar Black and a generic DVD drive hooked up to them.


Problem

When I turn it on, everything appears normal. The motherboard's post code display goes through what I assume is a usual sequence (it hangs on 25 for about 5 seconds, I'm not sure if that's normal) and then I hear the POST beep, and am able to get into the BIOS or start to boot from CD. However, somewhere between 30 and 60 seconds after boot, the red light below the CPU Fan Connector on the motherboard goes on, and shortly after the system powers down. If I try to start it again shortly after this, the shutdown occurs even quicker after boot.

All the case fans and the CPU fan spin up on startup and stop when the system powers down.

All of these seem to me to be indicative of overheating of the.... something, but I'm not sure how to go about testing which piece is overheating, or what to do about it once that has been determined. Anyone have any suggestions?

 

[kyeana]

sounds like the cpu is overheating. Try reseating the heatsink, cleaning off the old thermal paste, and applying some new thermal paste

 

[slomo4sho]

There are no other beeps? Normally the motherboard will beep in a particular rhythm if the CPU is overheating...

Your hard drive might be DOA or not connected properly.

it hangs on 25 for about 5 seconds

I am not sure what you mean by this. It hangs on 25?

 

[zylaxice]

Thank you both.

Kyeana: I'll try that. Is there something specific that I should use or avoid using when wiping off the old paste?

Slomo4shO: No, there are no other beeps when this occurs.

This occurs whether or not the hard drive is connected, and also occured when I connected a different SATA drive that worked fine in my last computer.

I am not sure what you mean by this. It hangs on 25?

I was trying to describe the boot sequence. It quickly flashes through a number of codes too quickly for me to read. Then it shows C1 for about a second, C3 for about as long, and then it displays 25 for about 5 seconds before giving the one beep and moving on. That's what I meant by "hangs".

 

[mrmez]

WOW, paragraphs dude...

Use them.