Get down and dirty! Get beneath your RV slide out and ask someone to flip the switch. You can see the motor turning and the other parts that are supposed to turn and move. If you're smart you can pinpoint where the problem is and repair it yourself.
What exactly seems to be the problem? Can you hear the motor running. If there is no motor sound then your motor for the RV slide-out is busted. Check the fuse or replace the motor to set it right again.
If it's broken you'll need to change it! I had a friend who's RV slide out broke because the front rollers were damaged. It cost him more than a 1000$ and took about 15 days to get it fixed.