Recent problems with Steam Games

I have noticed a new problem that I believe is just with games on Steam...not sure if its related to ATI card 5700 series or not..

Occasionally, the game will freeze, lockup...you can hear the sound and everything around you, AI characters, etc continue to move but your character/mouse just freezes, locks up, forcing a PV restart...alt/con/delete won't work.

Started with Mafia 2 and happened frequently with Saints Row 3..all drivers are updated and I turned off anti-aliasing too..recently, happened less frequently with SR 3 but it now happens with Call of Duty, Black ops...even left for dead 2, which ran fine a year ago, is starting to freeze/lockup...games will play fine lets say for 15-20-25 minutes then boom a lockup..

I believe I have only experienced this with games on Steam...

Would this be a Steam/ATI conflict, a Direct X issue, driver problem, graphics setting issue?

Since this seems to only happen with Steam games, could this be a ATI 5700/Steam conflict?

Someone on Steam Forums mentioned that the video card might be overheated, dusty, and needing to be cleaned..but non-steam games, like Dragon Age, have run fine with no lockups..

And at times on Steam, Saints Row 3, Call of Duty Black Ops will run fine for several hours...at other times, 5 minutes into a game, everything locks up and the computer freezes. everything in the game continues on, other characters, video and sound, but my character (my computer) freezes, forcing a hard restart of the computer..

Just can't figure out the cause, why it happens only occasionally and not all the time, and what the solution might be, outside of obviously getting a new and improved video card.

I'll give that a shot!

by the way, how do you disable steam overlay? that's not the same as unchecking Steam Cloud synch, is it?