Now , it is important to have a Display Port on the monitor, if you have a projet purchase...
On the graphics card , it is important too , have a display port or mini display port.
So check it... Because the Display Port is more fast, and you have a higher resolution.
Maybe your PSU are limited... Probably is functionnal...
So if you want keep a hardware .... very long time, the best is change de PSU...
Maybe more later....