Dell S2715H Monitor not displaying to the edge

Hello,

I just received a Dell S2715H monitor and I connected it to my OptiPlex 790. I had to go buy a DVI - HDMI cable because my 790 did not have an HDMI connection.

My question is why does the monitor not display to the edge of the screen. It only displays to about an inch from the edge.

Please tell me how to fix this.

Thanks, Daryl.