Have you done a repair of avast via add/remove? If you haven't done it, do a repair of avast and follow the instructions. Once repair has been completed restart your computer manually. If still that didn't solve it. Follow these instructions below:
1) Uninstall avast via add/remove and follow the instructions.
2) Download and run avast uninstall utility. This tool will let you know that this tool will run your computer automatically in safe mode. Click ok on both and follow the instructions. Avast uninstall utility is found here
https://www.avast.com/en-nz/uninstall-utility3) What is your previous antivirus prior to using avast? Download your previous antivirus removal tool from here
https://singularlabs.com/uninstallers/security-software/. First turn your computer in safe mode and run your previous antivirus tool and follow the instructions.
4) Install a fresh copy of avast from here
https://www.avast.com/en-nz/index. Once installed it will do a quick start up scan and once that has been done restart your computer manually.
5) Register your copy of avast.
Firstly, make sure your computer has got the latest SP. For Windows 7 is SP1 and for Windows 8 is 8.1 and it is fully updated with Microsoft Updates and patches.
