Eddy
7
I’m not giving up helping/trying to solve it that easily 
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Click on Start, run, type services.msc and hit enter to open it.
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In Services Console window, find and locate Windows Installer service.
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If the service is stopped, start the service and set it to “Automatic” or restart the service if it is already started.
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Reboot your computer and check if it solves the problem.
Ps:
This is a Windows problem and not a avast problem.