yeah the p4s suck a LOT more power than even the amd 64s do and they take a lotta current out of the 12V rail... so im also thinking that u need a new psu with stronger rails 
... try the ultra x-power supply (i think thats what its called )... it has the best 12v rail out there and its modular.. so u only connect the wires u need.. very space saving
... try the ultra x-power supply (i think thats what its called )... it has the best 12v rail out there and its modular.. so u only connect the wires u need.. very space saving 