PC shuts off while finalizing Windows 7 Installation

Hello, I know this issue has been posted before but none of the solutions are working for me (that or I'm doing it wrong).

I'm building a new system using Windows 7 Ultimate 64-bit (bought from my university's bookstore, not a burned .iso). At first, my computer powered off while I was installing Windows 7 on a fresh HDD (about 75% of the way through Step 2). Now I've gotten as far as installing Windows 7 and reaching the "Starting up Windows for the first time" screen, at which point my computer began freezing.

I read into the issue on these forums and saw that clearing the CMOS, changing the BIOS settings (specifically, changing the USB storage setting to "disabled"), removing USB devices during start-up, and swapping out an ATI graphics card had helped people. I've cleared the CMOS, bought a new Nvidia card with the intention of using it long enough to finish the install and then returning it, altered the BIOS settings, removing my USB mouse during startup, etc. None of these have worked for me, and now the computer is powering off entirely rather than just freezing. I've also tried the Windows 7 Startup repair utility to no avail--it claimed it found something, but when it rebooted I continued to have the same issue.

I have not tried updating the BIOS because my motherboard manual says I have to do that after the OS is installed (quite frankly, I don't know for sure how to do it before the OS is completely installed, either).

I think my system specs should show up on the left but, in case they don't, I'll make a list:

• Gigabyte GA-P55-USB3 LGA1156 mobo
• XFX Radeon HD4350 ATI video card/GALAXY GeForce 210 Nvidia video card
• Intel Core i5 750 Lynnefield 2.66GHz CPU
• ADATA 4GB (2x2GB) DDR3 RAM
• Corsair CMPSU-750TX PSU
• WD Caviar Blue 640GB SATA HDD
• WD Caviar Blue 320GB SATA HDD
• Sony DVD/CD RW IDE Drive DRU-830A
• HTC XT-1264 Heatsink

I have some ideas about other potential causes for the issue, but I can't really be sure. For example, my heatsink was listed somewhere as a "universal" heatsink. When I got it I found out that it isn't supposed to be comptaible with LGA1156 slots, but I got it to fit anyway so I figured maybe it would be OK. It also doesn't seem as though the heatsink is loose. I don't know if Windows 7 starting up could be causing the CPU to overheat, but I'm not hearing any warning beeps or anything like that.

Any help would be very much appreciated.

I thought through the installation process of windows the computer turns on and off by itself so it can make the changes, and configure/install quicker.

Correct me if i am wrong please.

Thanks,
Gamer

Well, yes, it does that, and it did that. But, it displayed a warning message before those "intentional" restarts and it came back on afterwards. In this case, the computer is just shutting off while trying to boot Windows 7 for the first time, and not starting back up again on its own. Sorry for the confusion.

The only few things i can really think of is that it would be a hardware problem. Like the power supply is messing up, the computer itself is overheating. stuff like that.

HonorGamer: That's what I'm worried about with the heatsink, but the way it's shutting down isn't really typical for overheating (at least what I've seen). I have Hiren's Boot CD, so maybe I could test the hardware that way. Or, I was thinking about installing XP to see if that works and isolate it to a Windows 7 issue.

myzr7: Thanks! :) Yes, I have tried safe mode, but when I do I get an error message saying that Windows cannot complete the installation in safe mode.

I don't think overheating can cause shutting down, just freezes. I threw that out there just because I could be wrong. It is possible that it could just be a windows 7 deal, so try and install XP and see what happens from there.

That's kinda weird. Will 7 work on only 1 stick of RAM?