For the past 1-2 weeks my desktop becomes unresponsive sometimes. The problem seems to happen as I load a page in Google Chrome; it could be any page though today it happened when I tried to load a page with Flash content in it. The problem is not consistent and there is no pattern. I can do a virus scan using some software (not antivirus installed--never needed that) but I strongly suspect it is some software I installed or some Windows Update. This is a very powerful Dell Optiplex 990 with 16GB RAM, so Memory shouldn't be an issue.

When the problem happens the cursor becomes spinning even over the taskbar and control alt delete takes a long time. Eventually I get a message that 'this program is not responding' with end/close and 'cancel' icon. But repeated end or cancel does nothing. Then the menu for ctrl alt del comes up.

The rest of the applications keep running fine though I can't get to them because the cursor is the wait-cursor.

What is happening? How can I find what exactly caused the problem? Thanks.