Clock movements are really very simple, when you compare them to electronics. Brass clock movements are generally not influenced by all but the most extreme static electricity, temperature fluctuations, humidity changes, or magnetic fields. Once all of a clock movement's wheels have turned 1 revolution, there is no reason why they shouldn't keep making those revolutions for at least 2 years time without service unless some physical change has come to them.
Unless it has been moved or jostled there is no reason to expect that any modern mechanical clock should develop any new problem after a week's worth of good running. If your clock stopped working properly "out of the clear blue sky," take a moment to double check the following:
1. "Is the clock hanging straight?"
Forget about how straight the clock looks on the wall. Use your ears. You should be listening for an even TICK TOCK (listen) sound. If you hear an uneven tick TOCK or TOCK tick (listen) sound, carefully tilt the clock one direction or the other. You can carefully move the bottom of the hanging clock to the right or to the left until you hear that even ticking sound.
2. Flat against the wall.
Make sure that your clock is hanging flat against the wall. There should be no space between the back of the clock and the wall. The clock needs to be hanging exactly parallellel to the wall.
3. Wind the clock fully.
Many times, clock owners will be afraid of winding a spring-wound clock too tightly. Don't be. You can't break the spring. Most mainsprings are about an inch-wide ribbon of tempered steel. Could you imagine breaking this with your own arm... by twisting it?? These springs will break under the stress of age, nothing more. Besides, there is a stop catch built into new mechanisms to provide safety.
Wind the clock until it comes to a complete stop. If you have a key, wind it until it goes no further. If there are weights, wind the clock until the weight comes all the way to the top. DO NOT LIFT the weight with your other hand. There should always be tension on the chain or cable which supports the weight. The cable won't break, you don't need to "help" it.
4. Shut-off switch
Check the shut-off switch and don't trust the markings that label that switch. Sometimes they can be confusing. If your clock is not cuckooing, try the shut-off switch in both positions regardless of what the marker says.
5. Where are your weights?
Make sure the weights are each hanging on the hooks correctly.
6. The cuckoo door
There is a little wire latch which sometimes gets in the way of the cuckoo door. Make sure that this is out of the way so that the door can open.