If your system was fine before adding new graphics card I'd try a different slot on motherboard or maybe re-install drivers, as it sounds like the new card is the problem. Otherwise the PSU could be going bad but 700W is plenty for this build.
That power supply should be plenty for your listed components. However it is an older OCZ and pre 2007 OCZ units had quality problems. That model is from 2006 when OCZ was more of a "do not buy" company. So it is very likely that unit could be failing. Any power supply degrades over time.