If you are not confident in your ability to diagnose the problem call a local garage door service company.
Garage door chain drive fix.
Make sure the tracks are aligned properly.
Located along the rail the chain an.
If there are some you can use a wood block and your hammer to fix the dents.
Slide the pulley toward the garage door until the chain is stretched tight then move it toward the motor until the middle of the chain touches the upper side of the chain arm.
This video from sears partsdirect shows how to replace the chain and cable assembly on a chain drive garage door opener.
A new front sprocket costs about 150 200 include the labor to install it.
The chain wraps around this sprocket as well as the gear and sprocket at the motor.
Press the remote or the wall mounted start switch listen to the motor and watch the movement of the chain.
Sprocket is at the end of the opener rail closest to the garage door opening.
Examine the metal tracks on the door for dents or bumps.