Whenever I try to play any source games (I've tried Half-Life 2, Portal, and Team Fortress 2), they crash. I start the game fine, and can run around or do whatever for a couple minutes, but then it crashes. What usually happens is the video freezes, the sound loops for a couple seconds, and then the screen goes black and the sound turns into a horrible screeching noise. I then have to reset my computer. Before it crashes, everything is covered in little red checkers, they're kind of sparsely dotted instead of solid. This has been going on for quite some time. Half-Life 2 used to work perfectly fine. I was able to play Team Fortress 2 one time successfully until I quit myself, but after that it's crashed every time. I just formatted my computer for other reasons, and hoped that it would fix this problem too, but it still crashes the same.

I have an AMD Athlon 64 3200+, an ATI Radeon 9800 Pro, and 1gb of ram, and I'm using Windows XP Pro.

Thanks.

I used to have this problem, and the reason was my processor and windows werent very well matched, It can also happen sometimes if your hard-drive is too full, With Steam you must accept that unless you have the perfect spec computer for the games, Its gonna give you a hard time, Most probably the format will sort it out, but other than that i suggest you do a steam compatability check, and also think about new graphics drivers, The latter would be the most effective most probably.