Graphics card and power supply's

Question about graphics card and power supply.I have a hp pavillion media center edition m1090n.Lately my monitor has been losing the signal(doesn't matter what I'm doing) like it goes into stand by mode but cpu is not.Event viewer shows nv/driver or display was caught in an infinte loop.I tried newer driver,changing power saver settings,checked bios temp(130)and card temp(80) ran full chkdsk and virus scans but it still does it.I'm thinking it's either the card or power supply.Power is original 300 watt.Like to upgrade both.Any help for power supply's that will fit my case and a good card around $200.


hp pavillion media center edition m1090n
win xpsp3
3.6ghz
3gb ram
Nividia 7950gt pci-e

Thanks for any help.