having random restarts with my asus mobo help me plz!!

my system:

asus a7v266
512 ram (2x256 different brands that sucks )
athlon 1.2
2 HDD
1 cd-rom , 1 cd-rec
live 5.1
gainward gf4 Ti4200
1 usb scanner
ps2 mouse & keyboard
300W PSU
winxp pro

the problem:

after getting the new card my system keeps restarting randomly, that usually happens when left idle for a long time and trying to do some action again(open a program for ex.)
i read in another thread about the system recovery settings and uncheck autorestart, that caused my system to freeze completely!! could it be the psu?? or maybe some bios settings i have no idea plz kind ppl help me!!! ((((

Does sound like the PSU.

Check the rated watts on the side of it.
the 3.3v line should be.....30
and atleast the same for the 5v rail.

Good Luck

hmm... the 3.3v is 28 A
and the 5v is 30 A...