Windows 7: ATI RADEON HD4670 Screen Resolution Issue

I am having a problem with setting my screen resolution with ATI RADEON HD4670. I can't set it bigger than 1600x1200, although my monitor gives a warning that indicates that it should be 1680x1050.
My system is,
OS: Windows7 Ultimate 32bit
CPU: Intel Core 2 Duo E4600 @ 2.40GHz
RAM: 2.0GB Kingston DDR2 266MHz
Motherboard BIOSTAR P4M89-M7B - VIA P4M890 Chip-set
Graphics Card: ATI RADEON HD4600Series(4670) 1GB
Hard Drive: 250GB SAMSUNG HD251HJ IDE



I have Catalyst Control Center installed with all necessary drivers and it is up to date.
Problem occurred after my electricity went off. When I started my PC, resolution was really low, so tried to set it to 1680x1050, but the options are as it is here:
http://i48.tinypic.com/vfdtfp.png
Can anyone help me fixing this please.
Thanks in advance.