If I might suggest, you may have been compromised. Try virus scanning your pc from a cloud based service, or, try disabling Avast ( don't uninstall it, just stop the relevant services ), and then install Microsof security essentials and do a full scan. One of the ways that some malware works, is by disabling installed anti-malware scanners, so the they can't be reported upon. Using a different product, ( and if the different product doesn't install or run correctly, be very suspicious), may get around this.