My Dell XPS 8000 (Win 7, i5-750) has become very unstable.  It freezes frequently, requiring me to reboot by shutting off the computer with the on-off button.  Sometimes it is a program that freezes, sometimes Windows itself.  This problem seems to be worse since the recent upgrade in Windows Live Mail-- which is one of the applications that often freezes-- but it was happening before then too.  CTL-ALT-DEL frequently does not bring up the Task Manager, or does so only after a very long wait, which is why I have to use the on-off button to reboot. 

I have cut back drastically on the programs that load at start up, because a major issue had been freezing if not everything had loaded (and it was hard to tell if everything had or not), but this has not eliminated the problem.

Thanks.

Steve Kamin