Cut your losses and chunk the Craftsman garage door opener. Get a Genie and you will never post a question about openers on this forum again. A little research on this forum will show you hundreds of posts about those badly engineered and cheaply produced monsters. There are probably more questions about them than anything else on this forum. I recommend the Genie "Excelerator". Opens twice as fast, quiet, has two lights, and extremely reliable. See the Genie link below. Here is a link that might be useful: Genie Excelerator at Home Depot

If it is stuck in the open position you will most likely find the trolley is jammed against the bolt just in front of the motor unit. You will need to loosen the chain enough to release the tension and then run the opener until the door closes. While the door is closed locate the 'up limit' on the side of the motor unit and turn this control 2 full turns in the opposite direction of the arrow printed on the cover. Tighten the chain.

If tapping on the unit restores function the first thing I would look for is a loose connection. BTW, Chamberlain makes most, if not all, of Craftsman openers.

Ok, gotcha now. If I were their I would pull off the cover and see if anything inside looks worn. Check out the gear, if there is a bunch of white saw dust looking stuff the gear is wearing on you and in need of replacement. Also look for ground up metal on top of the opener itself right next to the sprocket and on top of the gear. If this is the case you will need a whole gear and sprocket assembly. If all that checks out good the problem is probably in the circuit in board in which I would invest in a new opener rather than trying to repair it. The board is going to cost around 90 bucks and you can buy a new opener for about 150 bucks with up to date technology. No, On the way up if the door becomes obstructed in some way it just stops. Good luck.