You may want to delete a few files:
Under ...\<USER NAME>\Documents\Mount&Blade Warband\
delete rgl_config.txt, then restart Warband.
If that doesn't help,
A hidden file/folder under ...\Users\<USER NAME>\AppData\Roaming\Mount&Blade Warband\
delete controls.dat and perf.dat, then restart Warband.
The game will re-generate new versions of these, and hopefully those will work.
If that doesn't help,
go to the same place and try renaming profiles.dat to something else (this will lose your multiplayer appearance/login info, but if it works, then you can replace that...and if it doesn't work, just rename it back to its original name).