A quick fix would be to replace the .exe with one from gamecopyworld.com.
its not illegal and i know a few people that use the crack with legal versions to bypass the CD check so they dont have to fiddle around with media. In your case it would be okay to grab an .exe for WaW if you have lost the original.
Of course, as shiftstealth says you may have moved or removed the .exe entirely but that just gives a missing target error.
To check compatability mode you need to right-click the .exe
If you dont wanna mess around with .exe's then just uninstall and reinstall.