I don't play Combat Arms anymore (and haven't since about 3 or so years ago) so my information may be outdated.
Regardless of any Combat Arms updates, try updating your graphics card drivers. Outdated ones may have incompatibility issues with games and such.
Second, check your graphics settings in your graphics control panel (i.e nVidia to the nVidia graphics control). There may be a setting to default the resolution to the game's default resolution.
Lastly, make sure this isn't Combat Arms's problem. Does this happen on anyone else's computer or another computer you may own? Have you tried uninstalling and reinstalling the game?