3Gb should be plentiful. Doesn't seem to be a ram problem then.

Worst case scenario. You fried your gfx card and it has been unable to utilize it's maximum capabilities since. :P (I had it happen once. :< But this usually comes with excessive screen tearing and such.)

You should be able to test that though with 3d testing programs. There's also a possibility your ram is just buggered. Try 'resetting' your PC to force your ram to reset. *shrug*