PowerMac G4 Quicksilver random restart

i have a dual 1ghz PPC PowerMac G4 that will restart for what seems like no reason at all

my first thought was that it was over heating..i was right, so i took out the stock fan and replaced it with 2 custom fan that keep the cpu more than cool

the problem is that it will still restart randomly...anybody help

Powermac G4 Mirror
1 ghz PPC processor (2x)
1.5 gb DDR ram
160gb HDD(master-start up disk) 80gb HDD(slave-for time machine)
2 optical drives cd-r and a DVD-ROM
ATI Radeon 9000 Pro, 64mb VRAM

ok..well since nobody has any idea i think ill just take it to the apple store for diagnostics