New build boots up, turns off after 10 - 30 seconds

[funkmonk22377]

This is my first build. Did a whole lotta research and seen a couple other friends put together computers but I'm not sure what's goin on here. Problem:
New system boots up, goes through posts, then goes to screen saying awaiting system disc (haven't gotten my XP cd in the mail yet) or if I hit delete it goes to bios setup. After about 30 seconds from the time it first booted up it just shuts off. Even if I'm actively going through the bios menus the system will still just shut off after about 30 seconds. If I turn it immediately back on it might go off after 20 seconds. If I turn it on again it might turn off after 5 or 10 seconds. All the fans appear to be running alright. I tried turning up the speed of all the case fans (manual adjust) to the max, thinking maybe this was some kind of overheating issue but that made no difference. I've been operating with the side of the case off too, just in case there was a heat issue. Help!

Specs:
Antec Nine Hundred ATX Mid Tower Case
850W Real Power Pro Psu
ASUS P5N32-E SLI LGA 775 NVIDIA nForce 680i SLI ATX Intel Motherboard - Retail
Intel Core 2 Quad Q6600 Kentsfield 2.4GHz 2 x 4MB L2 Cache LGA 775 Quad-Core Processor - Retail
CORSAIR XMS2 2GB (2 x 1GB) 240-Pin DDR2 SDRAM DDR2 800 (PC2 6400) Dual Channel
Seagate Barracuda 7200.10 ST3250410AS 250GB 7200 RPM 16MB Cache SATA 3.0Gb/s Hard Drive - OEM
EVGA 512-P3-N801-AR GeForce 8800GT 512MB 256-bit GDDR3 PCI Express 2.0 x16 HDCP Ready SLI Supported Video Card - Retail
SAMSUNG 20X DVD+R 16X DVD-ROM 48X CD-R 2MB Cache SATA 20X DVD±R DVD Burner - OEM

[cmichael258]

Did you double check to see that the HS is fully seated on the CPU? Could be that the heat generated is too much for fans or an open case to help.

[Cricket]

Either the heatsink isn't installed properly (LGA775 heatsink installation tutorial) or that's a real low quality power supply and it's overheating and shutting down.

Cricket

[funkmonk22377]

Hey, thanks for the advice guys. It looks like indeed the heat sink was not fully and correctly seated on the processor.... two of the four screws weren't fully pushed into place. Turned out I had to press really, really hard to get them to click into place (had to get my body weight behind it... harder to push in to place than a RAM stick!). I was scared of this clicking sound occurring during screw-pushing, I thought it might've been the motherboard cracking... turned out to be the sound of the screws snapping into place. Just had to push hard enough. My hands hurt.
Seems like all's well now. Computer's been up and running for a full 5 minutes and no problems - hooray for online forums and troubleshooting!

[liambl]

I don't know who designed the LGA775 heatsink but it is a pain to get in. I hate doing them, the amount of pressure required scares me. I much prefer the AM2 heatsink clip.