Problems with applications crashing.

[worshipme]

I recently installed an extra 2gigs of RAM and a couple of extra case fans, and ever since some of my more demanding games (like the Crysis demo, in fact mostly the Crysis demo) often crash back to the desktop. I thought was probably because it's maybe not as stable with the extra power draw so I turned my CPU back to 3.2GHz and my GPU back to the stock settings and everything apart from Crysis ran fine and dandy. If I want to play Crysis, I have to lower my GPU to a 500MHz core clock and an 800MHz memory bus. Surely there's something wrong? I shouldn't have to lower my graphics card to below stock speeds for it to be stable, should I? Does anybody think it could be my PSU? I have this:http://www.ebuyer.com/product/109552
EDIT: I removed the 2gigs and unplugged an LED 120mm fan and it's now perfectly stable. Surely this means that it's my PSU? Any help would be appreciated.