I have two computers connected to a Dell U2711 monitor. A PC which is connected using DisplayPort and a Mac connected using DVI-D.

The PC displays 2560 x 1440 resolutions perfectly but when I try and set that resolution on the Mac it displays in an extremely fuzzy manner. So fuzzy in fact that I can hardly read the text on the screen.

I've tried the Mac out connected via DisplayPort (unfortunately the monitor only has one DisplayPort connection) and it worked perfectly. I also had it connected via DVI-D in the past and it worked then. For some reason it just does not work anymore.

I was wondering if this problem might be caused by a dodgy cable or perhaps not having the correct one.

Can anyone think of what the issue might be? I've checked out the DVI-D spec and it should be able to display resolutions of 2560 x 1440 correctly.