Windows 10 user here ... Mathematica runs fine !

I was "fortunate" to have to re-install my laptop with Windows 8.1. I reinstalled MM10.2 and it worked very fine but I was not pleased with the resolution of the fonts. Windows has quite some options so I played around with the display settings. I changed the setting for ClearType

http://windows.microsoft.com/en-us/windows/make-text-easier-read-cleartype#1TC=windows-7

or

http://windows.microsoft.com/en-us/windows-8/get-best-display-monitor

Then the problems started! MM10.2 took 3 minutes to start and showing the formatting notebook etc. Starting Help took forever and changing back the settings didn't help. After a re-install (again) of Windows and leaving the display settings standard I checked a setting called "Make text and other items larger or smaller") and that solved the grainy fonts in my notebook. MM 10.2 now starts within 2 seconds and the help pages are instantaneous.

Changing the Graphics driver didn't solve it for me but it seems that MM relies on defaults somewhere down in the Windows world which could be altered installing windows updates. By caution I now check the updates before installing and won't update any driver or update related to graphics unless I have to..

I hope this helps.. I use a HP Envy TouchSmart 15-K048ND (with SSD and 16GB RAM)

"I had to do step 6 before I could do step 5" - Same for me!

On mathematica.stackexchange.com i asked pretty much this question. Very fast somebody linked me to a 20 days older similar question that was asked, where someone answered he had had this problem and fixed it by graphic card driver updating. This reminded the asker of screen calibrating might be the thing. When I read that I was reminded too, but I didnt know how to undo screen calibration. Microsoft's help forum helped me through.