If avast antivirus will not open then following below step may resolve your issue..
- Click Start
- Select Control panel
- Visit Programs
- Click Uninstall a program
- Select Avast
- Select Repair.
When the process is completed, you can restart your computer.
If the above step does not help you to troubleshoot avast antivirus not opening issue then you can follow our blog to learn more about why wont avast open?