Try a repair of avast:
XP - Add Remove programs, select 'avast! Anti-Virus,' click the Change/Remove button and from the next screen select Repair.
Vista, win7 or later - Control Panel, Programs & Features, uninstall a program, select 'avast! Anti-Virus,' click the Uninstall/Change and from the next screen select Repair.
You may need to reboot after the repair.
What other security based applications do you have installed, anti-virus, anti-spyware, firewall, etc. ?
Whilst I don't believe this suggestion should make that much difference, it is worth a shot:
AvastUI > Settings > Troubleshooting > check the 'Load Avast services only after loading other system services' option.