random rebooting

[Fjod]

Bought a new system yesterday.

Gigabyte K8NXP-SLI
OCZ Powerstream 520W
AMD A64 3000+ S-939 0.09nm
A-DATA PC4500 Vitesta 2x512mb
GF6600GT PCI-E

I built it myself, and started it up just fine.
so when I tried to install Win XP Pro on it, it just wouldn't find my SATA drives, so I installed the OS on a PATA drive. worked just fine... until I tried to connect my SATA drives.
At first Win wouldn't even notice that the disks were plugged in. So I browsed the net for info, I found out that I had to Disable the RAID feature on the controller that housed my SATA drives. Did that and had to reinstall Win.
Now win finds my disks just fine, but another problem came up.
the computer just randomly reboots, I don't have a clue why it does it.

I have tried cecking the RAM for errors, disconnect my SATA drives (the system seems to work better w/o SATA drives connected)

but now I am totally out of ideas, what the **** is the problem?
Please, if anyone have any clue on ehat to do please tell me!

 

[montag451]

Try taking all non - essential hw out of the computer.
ie, disable onboard sound/NIC etc
Does it lockup/reboot?

Can you try another psu from a working system?
Run MEMTEST on each stick of RAM

Did you put thermal paste on the cpu?
Did you connect the heatsink/fan correctly?
Are the case fans pointing the right way? - you don't want them all pointing in or all pointing out!