Noticing a yellow triangle with and exclamation sign in the tray, I checked the Problem Reports and Solutions folder in the Control panel under Windows Problems. The message there was: "A problem with your video hardware caused Windows to stop working correctly" The problem event name is "live kernal event:", then it gives an O.S. version and a local ID. From what I have researched, it appears that it might have something to do with the driver, or else the system gets confusing information. This has happened before a much as a year ago, but it can be months between occurences.
My video card is an ATI Radeon HD 2400 Pro and according to Piriform's Speccy utility, the driver is atiumdag.dll (17.14.10.833) Not sure if this could be the problem or not.
Quite a bit of stuff in the Problem Reports log, but the computer seems to just keep going. A restart gets rid of the triangle, and a Dell Diagnositc a couple of weeks ago did not turn up anything video wise. Any ideas as to what causes this/