Have you tried an avast Repair ?
Try a repair of avast:
Vista, win7 or later - Control Panel, Programs & Features, uninstall a program, select 'avast! Anti-Virus,' click the Uninstall/Change and select Repair, click next and follow.
You may need to reboot after the repair.
- If that doesn't work try, a clean reinstall.
Not sure what OS you may be using, I have winXP, Win7 and this win10 labtop, and all display the avastUI > Settings window correctly.