First set the menu level to "Super User" (Window->Menu Level->Super User). Then try using "Delete All Registry Values" from the View menu. This will reset all your settings and the IDE state to default.
If that doesn't fix it, uninstall RobotC, go into install directory (usually C:\Program Files\Robotics Acadamey) and delete everything there (if anything); after that, follow the steps I outlined here
to delete any lingering registry values. Now reinstall.
If that fixes it, good, if not, I'm not sure what else to tell you.