Does sudo xrandr -q show 1366x768?
My output only lists 1360x768:
cavsfan@cavsfan-desktop:~$ sudo xrandr -q
[sudo] password for cavsfan:
Screen 0: minimum 320 x 175, current 1920 x 1200,...
Type: Posts; User: Cavsfan; Keyword(s):
Does sudo xrandr -q show 1366x768?
My output only lists 1360x768:
cavsfan@cavsfan-desktop:~$ sudo xrandr -q
[sudo] password for cavsfan:
Screen 0: minimum 320 x 175, current 1920 x 1200,...
You can use that same command to change the resolution to what your monitor will support - the output of the first command.
If you wanted 1280 x 720 (16x9) for example you would enter:
sudo xrandr...
Do you have an nVidia card? What is the native resolution?
This will display the possible resolutions and the top one should be native
sudo xrandr -q