Well, I've been running my first watercooled PC for roughly 24 hours now and am starting to suspect I had my first disaster on assembly!
On first assembly of the system, I had a pretty major leak onto the video card (6600GT). Since the system only contained deionised water at the time and I dried the card out thoroughly before using it I wasn't expecting this to be a problem. However, when running using the NVidia drivers (it's a 6600GT) I get white or pink snow in various places on screen. This doesn't appear when using windows standard drivers (although these are chronically slow at refresh rate), and didn't appear before I installed the watercooling. Doesn't appear in Bios either. I've tried running an earlier version of the drivers (66.93) which is supposed to fix this problem, but I either can't get them to work or they don't fix the problem