napy666,
I had the exact same problem with the blank scan pop-up window. I did two things that seemed to fix the issue:
1. I restored factory defaults:
a. First back up your settings just in case you need them: Open avast program window - Settings - General in the new window - scroll to the bottom and click "Back up settings"
b. Then stay in the same window and click on Troubleshooting - click on "Reset now".
2. Then Repair avast as already described here:
Open your "Programs and Features" from the Control Panel - right-click on avast and Uninstall/Change then Repair.
Doing these two actions seems to fix my problem and now it displays the scan results.
I hope this helps.
All the best,
Norbert
