when you say that you close programmes using the ctrl alt del why do you have to do this? if it is because the games lock the system it would indicate a graphics card problem, possibly a driver prob. try uninstalling the card and letting windows find it then re-install drivers etc, also check the refresh rate and settings. have the games been configured to use the graphics card?
A little bit more info is needed I think, what graphics card? full system spec? what games cause the lockup? are the latest drivers/patches installed?