Your pendulum clock is a precision instrument that you can repair when it stops working. Before starting any repairs on your inoperative clock, however, make sure that it is not still because of a rundown main spring or an unset weight. Winding the spring or setting the weight and gently moving the pendulum may bring your clock back to life.
Level your clock if it fails to run or if it stops running after having been started. It may have gone "out-of-beat" when it was moved without having its pendulum and weights first unhooked and removed. Check your clock with a bubble level and find where it needs to be shimmed.
Bend the clock verge back into position with a set of needle-nose pliers instead of shimming your out-of-beat clock. The verge is the wire from which the pendulum hangs. It affects the movement of the "escapement," which is the part of the clockwork that makes the tic-toc sound.
Check the travel of the pendulum. Although you may have levelled your clock from left to right, it may still be uneven from back to front, in which case the pendulum may be hitting the clock's back wall. Shim where appropriate.
Check the clock's hands if it continues to stop. After levelling it or bending the verge back into position, the clock's hands may be touching each other or the dial, creating friction and causing the clock to stop. Carefully bend the hands away from each other and from the dial to allow them to move freely.
If your clock's chimes are not in synchronisation with its hands, allow the clock to run for two hours. Many pendulum clocks have a self-correcting chime mechanism that will correct itself within that time. If the problem continues, pull the friction-fitted hands off their tubes and refit them to be in sync with the chiming.
If your clock was manufactured after 1965 and none of your repairs have brought it back to life, replace the entire clockwork. There may be damaged parts within the mechanism that need to be replaced by a professional clock technician. You, however, may be able to replace the entire clockwork at a lower cost than what you would pay the clockmaker to repair it. By doing it yourself, you may also benefit from any improvements that the manufacturer incorporated into the new clockwork. Unfortunately, clock movements prior to 1965 are difficult to find and older clocks may require professional attention.
Your clockwork will need to be cleaned and lubricated periodically. Professional clock technicians are trained to take your clock apart, clean it and lubricate it with specific clock lubricating oil. If you are going to oil your clock between professional cleanings, refrain from using a general purpose oil or a spray lubricant that will attract dust and gum up the works.