You could try renaming your user.cfg file to make sure there isn't anything in there causing an issue.
Some other things you can try:
There is also a startup problem when running the ATI tray tool's on-screen-display (it shows fps for any 3D application). If you have this tool turned on and the game fails to start, turn it off.
Triple buffering has been known to cause problems on some cards. If you are having graphics issues or are having startup issues, try to turn off triple buffering in your graphics driver options.
Sometimes the Evolve client can interfere with the game. If you are having problems and are running Evolve, turn Evolve off and see if things work better.
Depths of Peril, Kivi's Underworld, Din's Curse, Drox Operative, Zombasite, Din's Legacy, & Drox Operative 2