First deletion isn't really a good first option (you have none left), 'first do no harm' don't delete, send virus to the chest and investigate.
There may well have been more than one piece of malware at work here.
System Restore is unfortunately not 100% and can have unexpected consequences when used.
Try a repair of avast. Add Remove programs, select 'avast! Anti-Virus,' click the Change/Remove button and scroll down to Repair, click next and follow.
Personally having used system restore I would reinstall avast to ensure that you have a good install.
- Download the latest version of avast, 5.0.462
http://www.avast.com/free-antivirus-download and save it to your HDD, somewhere you can find it again (if you didn't save your last download). Use that when you reinstall.
- Download the avast! Uninstall Utility, aswClear5.exe
find it here and save it to your HDD (it has uninstall tools for both 4.8 and 5.0).
- 1. Now uninstall (using add remove programs, if you can't do that start from the next step), reboot.
- 2. run the avast! Uninstall Utility from safe mode, first for 4.8 if previously installed and then for 5.0, once complete reboot into normal mode.
- 3. install the latest version, reboot.