If certain program components and features are not working properly in Avast Antivirus, we recommend you repair your installation using the Avast Setup wizard. The repair process resets your software configuration by fixing or replacing program files which may be out of date, corrupted, or missing.
When you repair Avast Antivirus, some customized settings may be preserved, however, other settings may return to their default configurations.
Instructions
- Ensure no other application or antivirus software is running on your PC.
- Right-click the Windows
Start button and select Apps and Features from the menu that appears. 
- Ensure Apps & features is selected in the left panel, then click your version of Avast Antivirus, and select Uninstall.
- Press the
WinXkey simultaneously, then select Programs and Features from the menu that appears.
- Right-click your version of Avast Antivirus, then select Uninstall from the drop-down menu.
- Click the Windows
Start button and select Control Panel. 
- Under Programs, click Uninstall a program if you are using the default category view,
...or click Programs and Features if you are using the large/small icons view. 
- Right-click your version of Avast Antivirus, then select Uninstall from the drop-down menu.
- If prompted for permission by the User Account Control dialog, click Yes.
- When the Avast Setup wizard appears, click Repair.
- Click Yes to authorize the repair.
- Wait while setup repairs Avast Antivirus on your PC.
- When the repair is complete, click Done, or if prompted, click Restart computer.
- Avast Premium Security 20.x
- Avast Free Antivirus 20.x
- Avast Omni 1.x
- Microsoft Windows 10 Home / Pro / Enterprise / Education - 32 / 64-bit
- Microsoft Windows 8.1 / Pro / Enterprise - 32 / 64-bit
- Microsoft Windows 8 / Pro / Enterprise - 32 / 64-bit
- Microsoft Windows 7 Home Basic / Home Premium / Professional / Enterprise / Ultimate - Service Pack 2, 32 / 64-bit