kc,
Ouch! Take it easy on Avast.
First, make sure you have ALL the updates for Avast.
Do a manual update of the PROGRAM which will also update the virus database.
Run a full scan of your system using Avast set to "Thorough" and "Archives". Disable the System Restore function in ME so if a virus is found there, you can do someone with it which means that the infected file will be deleted along with the restore points.
Now, if no virus is detected by the Avast scan, run a spyware scan using either Adaware by Lavasoft or Spybot S and D.
You can find them at
www.snapfiles.com under freeware.
You do have something destructive going on.
You also have the option to "restore" to a previous point using the System Restore. This would eliminate any "non-virus" causes in case it is a system corruption of some sort. I would use the System Restore first before trying anything else before a "good" point is removed by time.
Good luck.
PS: Post has been modified for clarity.
Thanks Bob!