Just logged on a few moments ago. Avast, after updating and telling me I had 29 days left on my paid Internet Security, refused to respond. It hung and I tried to close system, but ended up shutting system down manually. I was not able to get online... etc. I am wondering if anyone else is having this issue?
I am running now in Safe Mode with Networking.
When Avast! was updating, was it updating the virus definition updates, or was it updating the program itself? Sorry you have to use Safe Mode with Networking to post here.
If it is the former, try to boot into normal user mode. What is the result? If the latter, then go and get this tool here, and uninstall Avast! first via Add/Remove or Programs and Features, and THEN run aswclear.exe from your desktop in SAFE MODE only. Begin by selecting only the most recent Avast! version, reboot, aswclear for the next oldest, reboot, aswclear for the next, and so on. http://www.avast.com/uninstall-utility
If using paid, be sure to save your license file somewhere safe, so as to be able to retrieve it later.
Remove all instances of other old, uninstalled a/v programs using vendor tools provided here: http://singularlabs.com/uninstallers/security-software/
Reboot after each run of vendor tool. Some tools, such as McAfee, must be run more than once to ensure all remnants left over are removed.
Use another computer to download needed tools and install programs if possible, and transfer said programs over to you(r) broken a/v computer. Get the version of Avast! you need from here: http://www.avast.com/download-software
EDIT: fixed typo.