I have a Kenmore dryer with the same problem every once in a while. Apparently, the dryer's electronic computer chip has a glitch. I can always fix it using the following two methods. If method A doesn't work, then method B works. Try method A first.
Method A.
1. Rotate all the controls back and forth at least once.
2. Rotate the timer knob two complete cycles.
Method B.
Unplug dryer for a minute or so to let the electronic brain reset.
Kirk
August 2010