My garage door will not close. If I detach opener and close 1/2 way manually, will not operate down ward. But if I close the door all the way manually the opener will operate in downward direction

SOURCE: Remote will not operate garage door opener from outside garage

Will the remotes work in the garage? If yes but not outside with the door closed you might have radio interferace with your remotes. You might have to chage to a your reciever and remotes to a different brand (frequency). Sometimes it is less trouble to change out the operator. Chamerlain changed frequency from 390 (old) to 315 (new). 

SOURCE: Remote Control closes garage door but does not open

It sounds like a case of your keypad losing signal strength enough that it cannot transmit through the closed door. If a new battery doesn't do the job a new keypad will.

SOURCE: Door won't close unless I hold the button all the way down.

make sure the eyes are clean and aligned if the opener thinks something is obstructing its path it will not close

SOURCE: Liftmaster 1/2 HP Garage Door opener won't open or Close

The shaft on these garage door motors are not direct drive systems. You'll have to open up the box to see what the actual problem is. I have had stuff like this happen where a gear just slipped out of place.

http://www.aaadooropeners.com/?gclid=CLH3wt628p8CFVZS2goduwSLYQ

Here is a link for a parts supplier. I don't know your model but it looks like most of the Liftmaster worm screw gears and drive gears are plastic so it's possible that one of them has cracked.

SOURCE: I bought a second hand Digidoor 1 with garage

You are receiving interference from the digi door. You will have to return this unit and go with a different one on a different frequency. Chamberlain makes a clicker that would work well with that unit. Thanks BB