What resolution are you playing at ?
What size is your monitor ?
and that graphics card isn't very good, sorry.
buy a new graphics card.
Or your PSU might not be giving enough power or dying.
What is your CPU too ?
I agree with fuggles in that chances are your PSU could be dying and that your graphics card is too low end for any serious gaming (I myself used to have a 9400GT).
I doubt it has anything to do with your RAM.
From how you put your problems, before most of the games mentioned could be played at a playable frame rate. Is this correct?