Piano strings are under a great deal of tension, which is supported by the frame, plate, pinblock, tuning pins, bridges and soundboard.  Anything which effects the position of these parts will cause a change in the tension and make the piano go out of tune.

Push down on he back end of the key, near the capstan.  If both ends of the key go down at once the key is broken.  If the back end of the key will not go down, a foreign object, like a crayon has fallen under it.  If the back-end of the key goes down and the front comes up, determine if the key or action is sticking.  Hold the key down in the back with one hand, raise the whippen with the other hand and release the whippen.  If the whippen drops to its resting position properly the key is stuck.  If the whippen stays up the trouble is in the action.

If the front of a white key binds on the keyslip, remove the keyslip and insert shims made of paper or business card stock in the appropriate places so that the shims will hold the keyslip away from the front end of the keys.

If the piano key plays the action properly, but is slow in coming back up, remove the key and ease both the front & balance rail bushings, or sand spots which bind to the adjacent key.

Hammers usually break in the middle.  To repair, first remove the butt or flange in a grand piano, in an upright piano use a flange screwdriver.  Remember, do not apply excessive pressure to the jack.  Apply glue, align the parts and press them together.  Remove excessive glue and wrap the joint with heavy thread.  The thread may be removed and the shank sanded and cleaned after the glue has dried.