@HelonMead, it's a very nice proposal but I don't even have any PC box to welcome such a graphics card! My only PC is a Microsoft Surface and my main computer is an iMac.
And reading the links posted by aminor00 and LR9215 doesn't give me that much hope that it's an easy fix. Anyway, if I could try it myself, it would be nice. Would anyone here be ok to let me run some tests on their own PC with TeamViewer? I don't think I need admin rights and a new blank user account would be probably enough.