If Avast antivirus is not opening on your website, then you can fix this issue using this troubleshooting:
1) Repair Avast antivirus using the control panel.
2) Check for new updates
3) Upgrade windows 10 (if new updates are coming)
4) Turn off the windows firewall.
You can read more at:
https://worldzo.net/avast-wont-open-on-windows-10/