It is possible that this is virus related,but from the description you gave,it sounds more like there might be something wrong with your computer that might be non-virus related.(It is hard to tell sometimes.)Has there been anything else happening with your computer that might point to malware?
If you can still get in to your computer without a freeze/reboot,it might be worth having a look in Event Viewer,it might give some info about what is happening.
http://windows.microsoft.com/en-ca/w...=windows-vista
When you open event viewer,a list of events should be summarized:Critical,Error,and Warning.Try viewing critical events and see if it has anything listed around the times and dates when you are experiencing freezes,etc.Please post back about anything you find,etc.