I upgraded to Windows 10 from 7 last night, and now my DisplayPort isn't working. Blank screen. I had to use an older 1080p monitor through DVI so i could get access to windows. I upgraded my AMD Drivers to the latest (15.7 i think it was). still no luck. Each time i connect my main monitor it comes up with a DisplayPort error in windows. Never had this problem before.
Although, i did find i tried updating to 15.7 in windows 7 and i had the same issue. But, i was still using the previous driver when i upgraded to Windows 10. So that was interesting..
As you can see from my below specs, i do use a 27" iMac as my main display through DisplayPort. From PC to iMac. iMac only acts as display. I have not had any major issues since i have had this setup going from 2011 to date.
My PC Setup:
The only thing that has happened similar in the past, i had to switch my GPUs around on my motherboard. I may try this tonight.