uninstall Avast. Use AVG that's what i did.
Thats for sure not the best way
It's many times better to help the team to solve this problem and probably help Avast! improving their products by removing a bug...
With Avast 4.7.986 running
first i would recommend to update to the last program version, or is there a reason not to do so?
actually there is 4.8.1201...
if you don't want to update to the actual program version you should try to repair you installation (via add/remove programs in the system settings)
do you use any other antivirus-program, firewall, antispyware...?