after upgrade

after upgrading from my old pc to new 1 *look at sig*
i did wat most ppl would do, do clean install
ok after i do clean install of windows xp
i install drivers everythign seems fine
then i jus surf around the net, play some games and BOOM my pc restarts on me wats goin on?? i dont overclock or n e thing, cpu temp. is 39C. , mobo temp. is 35C. , didnt touch voltages or n ething, only made my ram go from 333mhz to 400mhz cuz da mobo it self slowed it down when 4DIMM slots are taken
n e 1 want to help me? my mouse also freezes sometimes but my pc doesnt freeze jus the mouse cursor
i haf all the new drivers updated and stuff, flashed new bios

What are the specs on the PSU and did you run a pass of Memtest yet?

nope dont know how to run the memtest
my psu is ENERMAS 535W SLI-Rdy

also my computer seems quite slow.. when im moving items or extractin it is like super slow...