|And also maybe a full virus scan, and perhaps a freebie on-line too via Trend.com (their freebie Housecall).|
Disable system restore before running any scans; and re-enable after a reboot - when system is said to be clean...
Also - before re-enabling system restore - if anything is quarantined.. delete it first; then re-enable system restore.
If possible run the scan in safe-mode (with networking) too (both for local utility and the on-line one).
Other things to do/check:
Run a full scandisk/chkdisk routine and let it fix anything it finds... If problems persist... seriously consider copying "all" data etc. to optical-media (and ideally another external HD too); so that is system actually dies for whatever reason(s) your data is safe etc... This is also a good practice to observe at all times; regardless of state of laptop/desktop etc...
Did you per chance go anywhere on-line that may have dumped something nasty into the sytem; did you install or otherwise change the system as was?