Do you have or had any anti antivirus on the system?
If so which one?
What operating system?
Any other security software installed?
Have you tried a repair of avast?
If not, try it.
If you did, uninstall avast, reboot and install it again.
Control panel > software avast > remove (choose repair to try to repair it or remove to remove it)
After removing run the uninstall util before rebooting.