[Solved] New Build Shuts Down - Cause?

I just assembled a new build from scratch, no old parts. It booted first try and ran for about an hour before simply shutting off with no warning. It wouldn't immediately reboot, but after cooling off for a while, it booted again. This time it ran for a shorter period, then shut off again. This continues to be the pattern -- it will boot when rested, but won't run for long, then won't reboot until it sits awhile.

My first guess is that maybe the power supply (550W) isn't big enough, although I thought it would be. My second is that the CPU is overheating (I'm using the stock Intel CPU cooler). Any advice on how to determine the cause would be much appreciated.

Here's the system:

Intel Core i7 920 Nehalem 2.66GHz LGA 1366 130W Quad-Core Processor Model BX80601920 - Retail
Item #: N82E16819115202

ASUS P6T SE LGA 1366 Intel X58 ATX Intel Motherboard - Retail
Item #: N82E16813131386

OCZ Gold 6GB (3 x 2GB) 240-Pin DDR3 SDRAM DDR3 1600 (PC3 12800) Low Voltage Desktop Memory Model OCZ3G1600LV6GK - Retail Item #: N82E16820227365

CORSAIR CMPSU-550VX 550W ATX12V V2.2 SLI Ready CrossFire Ready 80 PLUS Certified Active PFC Compatible with Core i7 Power ... - Retail Item #: N82E16817139004

SAPPHIRE 100258-1GHDMI Radeon HD 4850 1GB 256-bit GDDR3 PCI Express 2.0 x16 HDCP Ready CrossFire Supported Video Card - Retail Item #: N82E16814102837

Seagate Barracuda 7200.12 ST31000528AS 1TB 7200 RPM SATA 3.0Gb/s 3.5" Internal Hard Drive - OEM Item #: N82E16822148433

COOLER MASTER Sileo 500 RC-500-KKN1-GP Black Aluminum Bezel, SECC Body ATX Mid Tower Computer Case - Retail Item #: N82E16811119192

Acer X233Hbid Black 23" 5ms HDMI Full 1080P Widescreen LCD Monitor - Retail
Item #: N82E16824009163

Microsoft Windows Vista Home Premium SP1 64-bit for System Builders w/ Tech Guarantee - OEM
Item #: N82E16832116677

SAMSUNG Black 22X DVD Burner Black SATA Model SH-S223B - OEM
Item #: N82E16827151187

Thanks in advance,

Mark

Well, when I check the temps in the BIOS setup, it's running up into the mid 40s, which is essentially at idle and seems awfully high. The CPU cooler installed with no trouble and seems to be firmly seated. I haven't been able to check the temp under load because it really hasn't run long enough.

Mark

40s in BIOS is pretty bad.

If the CPU fan is spinning, then the next step would be to pull the cooler and check the base. Did you leave something between the CPU and the thermal paste? Or did you damage the thermal wax pad on the bottom of the cooler?

check your temps IN windows. DO stuff. idle temps can be deceiving. maybe your room is hot and your case doesnt vent incredibly well.

I verified that the fan is running, then pulled the unit. The thermal paste seems to be evenly distributed and I can't think of anything that would be interfering between the two faces. (There isn't anything that has to be removed from the base of the fan, is there?) I was pretty gentle during the installation, so I can't imagine I damaged the base in any way.

Mark