Ok, sfc /scannnow is running as we speak. Hadn't heard of or been told about that before. I was thinking about memory, gonna have to remove both chips and try one at a time. System runs perfectly after I restart it four or five times to get rid of the blue screen stop errors so I can pretty much rule out fan. Hmmm, will work on memory. Thanks for the tip, I'll be hoping it simply bad system files! You guys are a godsend!

Sharon