Try editing the /etc/X11/xorg.conf file and in the section where the default depth is set put
only your resolution and remove the rest.
It should look smtng like:
Code:
Subsection "Display"
Depth 24
Modes "1024x768" "800x600" "600x480"
EndSubsection
just change it to
Code:
Subsection "Display"
Depth 24
Modes "1680x1050"
EndSubsetion
It did the trick for me. Hope it helps...