Sapphire 6870 resolution problem, only with HDMI

So today I decided I would switch from a DVI cable to an HDMI for my computer.
However, I found that when using my HDMI cable the largest resolution I could achieve was 1680x1050.
My native resolution is 1920x1080 for my monitor, and it has always worked for both DVI and VGA in the past.
When I go above 1680x1050 the picture does not take up the full screen, and instead is smaller than it should be and is centered with about an inch border of blackness around it.

Specs:

Windows 7 64-bit
Radeon HD 6870 1GB
Intel i3-2120 @ 3.30 GHz
Biostar Mobo H61MGC