Mark,

I know VLK does not wholly agree with what I am about to say, but I know that it has been done by other users and done with success.

Sometimes, if using an older version, and then updating to a somewhat newer version that does not work for whatever reason, and you uninstall again…the add/remove function of Windows does not clean out the old Avast files fully.

Try downloading a copy of AVCLEAR from the Avast site and use this uninstaller first. Then try to install the newer Avast 4.1 Home Edition. Insure that all other non-essential programs are shut down whether they are Windows programs or not. Just leave Explorer and Systray running.

If this does not solve the problem, then I must yield to our Grand Guru VLK for further guidance. ;D

Good luck.