New System, Random shut down, no OS -- HELP!

[Garg11]

Ok so im building a new system, its my 1st time everything is going well till i attempt to Install Vista (64 Ultimate). the system just shuts off whenever it wants to. I got all the way to the restart after the Vista installation then after i restarted the PC shut down while setting up. Now i have to reinstall but the system keeps shutting down. Average times span from 5 secs to 20 mins.

Anyone know what ive done wrong?

System specs are:

Newegg.com - ASUS P5N-D LGA 775 NVIDIA nForce 750i SLI ATX Intel Motherboard - Intel Motherboards

Newegg.com - Intel Core 2 Duo E8400 Wolfdale 3.0GHz 6MB L2 Cache LGA 775 65W Dual-Core Processor - Processors - Desktops

Newegg.com - pqi TURBO 2GB 240-Pin DDR2 SDRAM DDR2 533 (PC2 4200) Desktop Memory - Desktop Memory

Newegg.com - HIPER HPU-4M880 880W ATX12V / EPS12V Power Supply 100 - 240 V UL, CE, CB, TUV, FCC, CSA - Power Supplies

Newegg.com - Western Digital Caviar RE2 WD3201ABYS 320GB 7200 RPM 16MB Cache SATA 3.0Gb/s Hard Drive - Internal Hard Drives

I also have a WD 320 IDE Hard drive

and an old Nvida 6300 graphics card freak: i know but im broke atm and saving for some SLI compatible cards)

Other than the random power downs the PC is running nice

 

[KSoD]

Hello,

Is the heatsink mounted properly? Do you have enough thermal paste? Have you tested the RAM? Is the RAM fully seated? Have you tested the system with only the mobo, cpu, psu and GFX card?

Cheers,
Mak