Having the same problem. The only solution is a full UNINSTALL of Avast. Short of that, rebooting from a complete power down does not fix the problem.
I log in, and open control panel (had to place a shortcut on the desktop), UNINSTALL Avast. Restart the computer and everything works well.
Did better this time, the install lasted almost a week before taking a header and crashing my computer.
Guess I need to find another solution because I don't live to UNINSTALL and REINSTALL software unless you folks have a solution to the constant crashing.