I upgraded to Vista Ultimate a couple of days ago, from my XP SP2 installation, by doing a reformat and going from scratch. I've been having some trouble running games. I've been playing Portal, specifically. It seems to happen at convenient times, so I'm struggling to pinpoint the exact cause, but I can't help thinking it's my video card. eg. If I open up the game, then as the company logos appear (Valve, etc.) I click my mouse once, the game appears to minimize, then reappear as a black window, then minimize, and keep doing this for a while until 'hl2.exe stops working'. If I leave it, or press 'Esc' instead of clicking, it goes to the menu fine. Then, if I try to load a map, when I double click on it, I more often than not get a blue screen. I've had the following blue screens: - PFN_LIST_CORRUPT - IRQL_NOT_LESS_OR_EQUAL 0x0000000A - One without a specific message: 0x0000007F Now doing some research, a lot of people appear to get these messages due to faulty RAM, but I've memtested this RAM a few times through and have had no errors whatsoever. It's good quality RAM aswell. I've tried the 3 most recent ATI Catalyst driver versions, and they appear to make a difference, but no solution. ie. I install an older version, and it may work, but then give me a new blue screen. Chances are that's just coincidence. I have a feeling it's a problem with my video card itself, so was just looking for opinions or guidance. Sucks if it is, as I just got this card RMA'd a few months ago, and the one they sent me was supposedly brand new (chances are it was just refurbished though).