Hello. As I already said, I'm currently using Windows 7, all updated (Service Pack 1 indeed).
On that computer, I had no other antivirus than avast! Free Antivirus, this is the first time I get a problem with it.
The first time I saw the problem, I tried a system restore, which brought back the version 2015. I updated to the 2016 version, and the problem appeared again.
I didn't try to repair anything else. I'm going to check that.