The instructions will help quite a lot right now:
1) Typical Timex manual says to re-set timer, press MODE and PROG buttons together.
Compare this information with your instructions.
2) Look on instruction sheet for timer model number, and then add a comment with your model number so I can identify timer manual and possibly post answer that fits your product.
3) Look on instruction sheet for company information.
Timex timers come with standard 1 year limited warranty:
Following phone might work: 1-800-919-3101
4) Scan your instruction sheet into jpg format and then add a comment with link to that jpg, then I can give you best answer for that specific timer.http://www.fixya.com/support/r6568559-post_photograph_fixya_questions_answers
5) Buy another timer, and return broken timer in new package.
6) Use circuit analyzer to test outlet for line noise and ground fault that affect timer electronics.
7) Buy another brand of timer altogether:http://waterheatertimer.org/Woods-timers-and-manuals.htmlhttp://waterheatertimer.org/GE-timers-and-manuals.html
Add a comment with your experience so others with same-similar problem can benefit.
Also take advantage of fixya expert assistance live.
For a price, expert works with you while you work on timer or any do-it-yourself project.
Fixya is always less expensive than a service call.