Craftsmen garage door is not opening. It started

The gears are all the same with the exception of the belt drive units that have a different top sprocket , you can find the part # on the internet simply by putting in the model # of your opener and identifying whether you have a belt drive or chain drive machine , you can also find the part on Ebay by putting sears/liftmaster or chamberlain sprocket gear assembly in the description ....All 3 of those models are made by Liftmaster being the main Brand ! Liftmaster manufactures the sears craftsmen for Sears and also goes under the chamberlain brand name that k mart and Home depot and Lowes sells ! Liftmaster is the worlds largest manufacturer of garage door openers and all 3 machines are interchangeable with their parts ! Hope this helps you Sincerely Glenn

You have a stripped drive gear. Remove the cover from the motor unit and you will find white sawdust all over. The part number for the gear kit is 41A2817 and is available at any good door opener service company. It comes with instructions.

Remove the cover from the motor unit and you will find the drive gear has stripped. White sawdust all over. The part number for the gear kit is 41A2817 and it comes with instructions. It is available at any good door opener service company.

SOUNDS LIKE A BAD GEAR KIT

IF THE CHAIN MOVES BUT THE DOOR DOESN'T IT WOULD BE THE TROLLEY RELEASE. IF THE CHAIN DOESN'T MOVE IT WOULD BE THE GEAR KIT.
HOPE THIS HELPS

Make sure you put the black cup back on the end of the motor shaft and that it is pressed all the way on. Make sure the RPM sensor is plugged in. If neither of these are the issue, then you probably did not have the motor shaft pushed all the way back when you tightened the coupler after replacing the worm gear. Loosen that coupler up and from the front of the motor (opposite end in which the coupler is on) push the shaft back as far as it will go. Hold it there while you tighten the coupler back up and then try it.

You should also loosen the chain enough that you can remove it from the sprocket above the motor. Now with the door closed and everything else attached run the motor until it runs clockwise and stops. Replace and tighten the chain. Some adjusting of the up and down limits will be required.

Unplug the unit and remove the cover, usually eight screws, if you see a lot of white dust in the cover check the nylon drive/worm gear, they will need to be replaced.

You should check the gears inside the box, After years , the gears get dry and die, you can by online or from Sears the kit and replace the old gears. I just changed mine...not too difficult :) .

Loosen the inner nut on the trolley. (That is the lock nut). Then tighten the outer nut on the trolley to increase tension. The outer nut on the trolley is closest to the garage door. The chain tension should be 1/2 inch off the rail at midspan. (The chain is fastened to a threaded bolt on to the trolley. The threaded bolt has an inner and outer nut). Hope this helps.

When mine did this, it was because the nylon gears that drive the chain had stripped. My wife had to live without the opener for a week or more, but I was able to find a new gear kit online and replace the damaged gears. It wasn't difficult.
The other option is to buy a new opener.

do not understand what you mean by can't reprogram openers, How old, Dip switches inside. Security plus. Need more info.