Mini mac with 24inch samsung?

Hi, i am currently using a mini mac with hdmi with a 24inch samsung screen. I'm not sure what i have done, but the picture quality has beeen affected. In system pre / display, i have it sey on 720p , 60 hertz , standard rotataion. Although this isthe best fit on my screen , the picture quality seems slightly blurred. This frustrating as it was working perfectly. I have changed hdmi leads etc. I need to try to go back to original settings...please help !!