I've been having EXACTLY the same problem for 3 days now!
I've tried just about everything, the full avast reinstall, using the aswclear.exe to remove avast, even removing all 'avast' registry entries before reinstalling. I can run avast! and perform a system scan (never returns anything), i just cant use the on-access protection. only ashdisp.exe and aswupdsv.exe are listed as running processes.
Avast! 4.8.1282
VPS 081117-0 (compiled 11/17/2008)
I use the standard windows firewall, along with the firewall built into my modem-router
I am not using any other permanent security tool, although i have tried out a few other scanners recently.
I have had several very odd issues recently including:
my paging file seems to be resetting itself every time i restart
I cannot update windows from the microsoft website.
I was seeing very strange folder permissions for my entire hard drive
I've run microsofts Windows Malicious Tool Remover, updated avast, run Malwarebytes' Anti-Malware and tried many other things. Either this is a nasty virus, or i'm suffering from a very corrupt windows installation all of a sudden.
please help!