Resolution Help !

So, im trying to access 1280x800 resolution or what ever it is on crossfire. I have 19 inch monitor and its Screen size max = 1337x768 . how ever i can't reach this resolution in crossfire but my brother can :\ . I've tried doing it the system data way but did not work .

I have AOC N941SW monitor wide screen 19 inch.

My brother has HANG Monitor Same size also wide screen .

He has Windows 7 ultimate 32 bit i have windows 7 ultimate 64 bit .

Why can't i reach this resolution -.- .

and? my brother can get it but i cant -.-