9800gtx+ wid CoolerMaster 650W - errors and frequent lockups while playing in Full HD

hey all, been a while since I posted here. I recently upgraded my monitor from a 17' LG flatron to Benq's 24' 3d LED 120 Hz monitor. Earlier, i used to game at 1280*960 res but now with new rig, i am playin @ 1920*1080. Prob i m facing is tht when i try to max out all the latest games out there, i get frequent lockups, black screens & then eventually the game recovers with errors in my eventviewer for nvidia. I am not sure if this is a problem with the card or the PSU. this is only a prob when i try to max out the games on full hd - if i lower the settings, i dont get the freezes & crashes. i can understand that the card is old and so it mite not be able to handle it but want to know if its only the card or the psu.

I am anyways planning to upgrade to a gtx570 and also feel that the current psu will just not cut it for that beast. planning to upgrade to corsair tx750 watts. that should be enuff, rite?

so welcome any suggestions on trying to isolate the problem with my current rig.