What are your resolution settings? Could they be accidentally huge?
Looks a bit like when my AV/firewall asks is it ok to let E: D access the Net, this pic seems more extreme though...
I have set E: D to 1920x1080 fullscreen, but when this happens I see only a Launcher window-sized part of the screen, at 1280x720 resolution. Have to reassign the correct settings manually again.
I had something similar occur when I had toggled headzoom or something I found if I pressed the key for one of the 3 UI interfaces it pulled me back out of it
Carl
You don't have Magnifier or something similar enabled do you?