It depends on exactly how it's not working and how old it is.
The first thing to know is that a reset only occurs if you push the tiny reset button in and hold it in for 30 seconds.
Make sure it is then set correctly:
http://www.mistking.com/images/timer_manual.jpg
If the Mistking isn't coming on when it's supposed to, first make sure that the outlet that the timer is plugged into is working by plugging a lamp into the outlet.
Remember, if the outlet has no electricity, the Mistking timer will still display everything because of it having a battery backup.
If a lamp lights in that outlet, plug the Mistking plug into the same outlet and see if it works.
If none of these things fixes it, send a message to Marty.