Hmmm… maybe a similar topic http://forum.avast.com/index.php?topic=25822.0
Use this tool to scan your PC - http://www.f-secure.com/blacklight
You probably still have an infection, probably a rootkit on your system that is killing avast.
See http://forum.avast.com/index.php?topic=26554.0
http://forum.avast.com/index.php?topic=25941.0
http://research.pandasoftware.com/blogs/research/archive/2006/12/14/Rootkit-cleaner.aspx
http://www.f-secure.com/blacklight/try_blacklight.html
After running the above rootkit tools if nothing is found try these.
If you haven’t already got this software (freeware), download, install, update and run it, preferably in safe mode.
AVG anti-spyware or SUPERantispyware or Spyware Terminator.