Trouble with my newly built computer.

[LimpGimp5564]

After a few weeks on waiting parts to arrive I've finally gotten my new computer put together. But now I can't even get the thing to work. Well really it worked fine for the first day. Right after putting it together it booted up perfectly fine which shocked me since this was the first machine I'd ever built. Second day of running it though, I was installing a bunch of programs and some windows updates. Now it kept giving me reminders every 10 minutes to reset the computer so the updates could take effect but I postponed it several times because I was leaving soon. I just assumed it would restart itself while I was gone since it had a five minute counter every time I postponed it. Anyways I went to pick my girlfriend up from work and when I got back the computer had not started again like I had expected it to. I turned it on and everything seems to boot fine but after just a few minutes the whole system shut down. I could turn it back on but it wouldn't sync with my monitor or whatever the correct term is. After messing with it for an hour or so I gave up. On random occasions it would actually work for a few minutes before shutting off again. When this happened I went into the BIOS and checked the temperatures of everything, and nothing seemed to be running hot, but even when I was just watching the temperatures it still would shut off after just a few minutes.

Currently, I gave it to my tech buddy who has been looking over it for a few days now and he's convinced its not my power supply or RAM because he replaced them with parts from his own machine to test it out, and it did the same thing. But I thought I'd get the opinion of some others on the matter of what the actual problem might be.

Here are the specs:
CPU: Intel Core 2 Duo E6850 Conroe 3.0GHz LGA 775 Processor
Motherboard: MSI P6N SLI Platinum LGA 775 NVIDIA nForce 650i SLI ATX Intel Motherboard
Power Supply: OCZ GameXStream OCZ700GXSSLI ATX12V 700W Power Supply
RAM: G.SKILL 2GB (2 x 1GB) 240-Pin DDR2 SDRAM DDR2 800 (PC2 6400) Dual Channel Kit Desktop Memory
Hard Drive: SAMSUNG SpinPoint T Series HD501LJ 500GB 7200 RPM SATA 3.0Gb/s Hard Drive
Video Card: EVGA E-GEFORCE 8800 Ultra 612MHZ 768MB 2.16GHZ GDDR3 Dual DVI-I HDCP HDTV

[Chazell29]

Since you were downloading some Windows updates, would it have been possible for the PC to shut down while you were still downloading some Windows Updates causing some files to become corrupt and the OS no longer work? Thats the only thing I can think of, and a fresh install of Vista might fix it. See what some of the other members think though about it, and about my post before you take my word for it.

[LeftyAce]

You can get into the BIOS just fine?

I don't think it's a hardware problem. Since it's a fresh install anyway, I would reinstall windows, and reboot when it wants to.

[LimpGimp5564]

Well actually, its only on a few occasions that I can actually get into the BIOS. Most of the time when I turn the computer on it doesn't seem to send a signal to my monitor and while everything seems to power up just fine all I have is a blank screen. Every once in awhile though it will actually start up and run for a few minutes, and when this happen I can get into the BIOS or even let it boot into windows but then seemingly randomly the whole machine will just turn itself off.

[LeftyAce]

Oh.
Next time you get into the bios, check the CPU temperatures. Just watch them 'till it turns off. If they are steady at around 40 degrees C or below, you're fine. If they rocket past that, then you have a cooling problem and need to reinstall the heatsink (the new intel heatsinks are really hard to get on right). Here's a link with instructions/tips: Intel 775 Stock HSF Install Guide

If it's not an overheating problem, try this to narrow down the possible culprits: http://forum.pcmech.com/showthread.php?t=168456
When you do that, you must remove the motherboard from the case.