You can find DIY repair guides for garage door openers on Sears PartsDirect: searspartsdirect.com/diy/symptoms/garage-door-opener-repair/1234637
The first thing to check is that the trolley cord is not pulled. In most cases, if you pull the trolley cord and then run the unit when it comes back into contact with the trolley it will lock back in with the door on it's own.
In some cases, inaccurate travel limits are the problem. Adjust the travel limit settings, following the instructions in your owner's manual. If you can't adjust the travel limits, you may need to replace the travel limit switches or the logic board. Make sure your safety sensors are aligned properly. You'll find the ways to check all these things in the troubleshooting guides below:
These two troubleshooting guides and videos may help you:
How to make force adjustments if a garage door won't open or close video: searspartsdirect.com/diy/article/how-to-make-force-adjustments-if-a-garage-door-wont-open-or-close-video
Garage door won't close/safety sensor troubleshooting video:searspartsdirect.com/diy/article/garage-door-wont-close-safety-sensor-troubleshooting-video-lights-blink-10-times
For repair, you can call Sears Home Services at 1-800-4-MY-HOME. If you need a new model: sears.com/tools-garage-door-openers/b-1024121?searsTab=true