I have to say I am also having problems with Avast (Pro) and Windows 7. I have three machines in different locations that started having problems.
Some info from my troubleshooting:
It started after the machine began acting weird during a session. Some programs wouldn't open, PC started running really slow. Rebooted the PC and after the restart, it sits at the login screen with Welcome and the spinning circle. Other times, the welcome goes away and I get a black screen with just a cursor. No commands work, nothing.
After hours of troubleshooting, I performed clean startup of the PC and got it to load Windows. I then started turning services back on, 1 by 1 until I found that if both Avast services are disabled, the problem goes away.
A full uninstall/reinstall seemed to help the problem, but I worry it will return.
At this point, I have found several posts explaining the same thing through Google searches. Not sure if a Windows update screwed something up with Avast! or if an Avast! update is to blame.
PCs are all Windows 7, Two Dell and one HP.
Thank you