Hi Instant_Classic,
To check for virus activity causing a problem, run avast! virus cleaner:
http://www.avast.com/eng/avast-virus-cleaner.html
Also try a scan with DrWeb CureIT!
If you can’t run either program, try renaming the .exe and see if that helps.
Try uninstalling avast!, then reinstalling. Select the option to schedule a boot time scan when requested.
If still having problems, post a HijackThis! log.