i think this has something to do with DPI Scaling. my friend has also experiencing the same problem, not just Arcmap but also with some other programs as well, with his newly acquired windows 10 laptop and we are trying to resolve the problem. i've googled it and found this info on the net. perhaps it could help you as well: pls follow this link... https://geonet.esri.com/thread/170386 or this http://www.tenforums.com/tutorials/5990-dpi-scaling-level-displays-change-windows-10-a.html