Restarts and hard time starting

[Budder712]

I just decided to redo my computer and bought all new but my Hd ,DVD drive and soundcard and now since I have put it all together I have problems getting it to start up and when it does it goes for so long and then will restart at random..I have double checked all my connections and made sure everything is seated well and in right slots and now am at wits end...any ideas on what to look at or what I may have done wrong..

specs of computer
Case  ATX mid tower
Power Supply Power King 650 Watt SLI Gold ATX PSU
Motherboard ASUS P5VD2-VMSE Core Duo Socket 775 VIA Chipset 1066FSB DDR2-667 PCI.e
Processor Intel Pentium 4 651 3.4 ghz - 800 FSB
Memory 4 GB DDR2 Kingston 533
Hard drive  Western Digital 120GB Ultra ATA 7200 RPM
Video card Ge Force 8600 GT 512m ddr2
Optical Drive BenQ Dual Layer/format 16x DVD writer
Sound Card Sound Blaster Audigy 2 ZS PCI

Thanks in advance for any help I can get

[homer]

did you reinstall your OS?

[Budder712]

Yes reinstalled the OS

[homer]

did you use thermal paste when you attached the heatsink? is the heatsink correctly seated? it sounds like an overheating issue. what is your CPU temp?

[Budder712]

it was assembled when I purchased and was put together with arctic silver 5...and case runs at around 58..3 case fans and Asus silent Knight heat sink fan on chip...Ty again for your help..has me checking things close and means allot

oh and OS is Windows Xp Home

[homer]

http://www.memtest86.com/

download and run memtest. this will test your RAM for errors. if overheating is not the issue, the next suspect is the RAM.

[Budder712]

ty again