My avast was set at the computer shop to automatically turn off computer after scan. I have looked on every link and can’t find where to change this setting so the computer will stay on.
You need to open the settings for the scheduled scan that you are running.
AvastUI > Scan (icon) > Scan for viruses - from the next screen, from the drop down menu select the scan.
Now click the Scan Settings at the bottom of that screen > Scheduling > Uncheck the Shut down the system after the scan finishes.