i have a problem.

i'm using Sapphire HD6950 2GB DDR5 + Samsung B2230 using the hdmi cable. i wanna ask, why i can't set my screen resolution to 1920x1080. Or HD screen.

i mean, actually i can. but the result is very bad. like the screen is smaller than my monitor. it got black space at outside the screen.

can anybody tell me what i do wring? thanks in advance. anyway, i had to use 1680 x 1050. and it result fit the screen, but the word seem blur a bit. that's all. thank you.