1. My first thought is heat. An overheated machine can do many odd things like this. Pull the case cover, point a fan at the internals for a test.

2. Pests and Parasites.
A recent post found the copy and paste function had been hi-jacked. Use to the Anti-Parasite Suite I note at http://reviews.cnet.com/5208-6132-0.html?forumID=32&threadID=1313&start=0 cleared that pest out. The Antivirus didn't catch it since it was not a virus. CWSHREDDER has moved to http://www.spywareinfo.com/~merijn/cwschronicles.html

It's your choice for your machine to be Parasite free.

3. Is System Restore to yesterday an option.

Bob