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Please try updating the Intel® graphics driver, you can download it at the following link:
thank you for your answer. I have downloaded the driver from the link but unfortunately it shows the exact same problem (bandwith error, again which is not true because it worked perfectly fine with the older driver...).
In fact, the driver that windows installed during the upgrade process seemed to be already a little bit newer than the one that you suggested:
downloaded driver: 22.214.171.12400 from 2015.10.01
from windows installed: 126.96.36.19931 from 2015.11.18
It seems that I do not need a newer driver with reduced functionality, but rather a driver from around july/august 2014 that just works...
So.... thanks anyway, but I still need to get my 27" screen working with its native resolution again
Any help still very appreciated!