Try running your system with one RAM i.e. the one which is plugged into the undamaged slot.
a)

If your problem is gone; well, you might you've to get that slot repaired. Though, I think that's a kind of work for which most engineers don't take the risk. They'll suggest you to get a new mobo. But, I think (if that's the case) you should sell your 512*2 RAMs and get a 1 gb RAM instead.
I know, that'll mean lower performance; but, in the other solution, you'll have to spend some money.
b)

If your problem still persists; well, give me some more details.