Can't change resolution [Windows 10]

[Slimez]

So I recently built a computer for a friend of mine and I'm trying to set up the 4k monitor, but It's only running on 1024x768. When I hit "apply" in Windows to change to 4k resolution, the screen just goes black for a while, then it goes back to 1024x768. Same thing happens with any other res (including lower ones). This is when monitor is connected with mini displayport 1.1 but when it's connected to DVI, I can change resolution just fine (up to 1080p).

So... suggestions?

[beneficialq]

Graphics card? 

[Slimez]

Graphics card? 

R9 295x2

[beneficialq]

do you have all the proper graphics drivers installed?

[Slimez]

do you have all the proper graphics drivers installed?

Yes. Even tried reinstalling.

[beneficialq]

Yes. Even tried reinstalling.

Can games be run at 4k no problem?

[Slimez]

Can games be run at 4k no problem?

Haven't tried, don't have any games on it. I have stress tested the GPU for 30 minutes fine though (I think it was a 4k stress?).

[Slimez]

Anyone?