I am having the same issues with Windows 10, it really does not work well for high dpi screens currently. All suggestions I found (Stackoverflow etc.) are just more or less functional workarounds that at the latest stop working when adding another monitor to the setup. Is there some timeframe when this can be fixed?
It is a shame that a modern and unique software like Mathematica still does not have proper high DPI support on Windows and Linux as it does on OS X! I hope this will be fixed in the next version!
the problem remains even in the newest version mathematica 11...
I think that the problem will be fixed when they decide to write the GUI using the QT5 libraries instead of the QT4....but In version 11 they are still using QT4 :(
Are you sure that your graphics card works well? Do other applications work fine?
The graphics card seems to be in perfectly good shape, all other applications I have been using work fine. The text in Mathematica is still readable (see screenshot below), but I did not expect this lousy quality.
Have you tried checking the resolution settings in the 'control panel' >> 'Display' area? I often have to adjust settings her when using a second screen - the Lenovo screen is too crisp to map easily onto an external monitor. Roger Dench