The first thing to do is verify that Avast is listed in your “Startup” programs

Click on the Windows world ball, type “Startup” and then click on “Startup Manager”.

If Avast is listed there then check the startup path.

It should be C:\Program Files\AVAST Software\Avast\avastUI.exe

The “regkey” should be "HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run"