I've found the solution.
The problem was that xorg.conf wasn't correctly configured for my monitor.
The monitor requires a refresh rate of 60, and I don't know what frequency my xorg was sending.
So, I just added these lines to my xorg.conf and now the image works great om my monitor:
ModelName "LCD Panel 1280x1024"
HorizSync 31.5 - 67.0
VertRefresh 50.0 - 60.0
Thanks everybody for the help.