I have a totalline thermastat. Model p4740100. It is frozen on one setting and will not respond . The A\C still works but I cannot change setting and is programed on one setting not the 4 setting available.

Turn off power.
Remove batteries if so equipped.
Wait 5 minutes
Replace batteries with new ones if so equipped.
Turn on power.
If this solves the problem OK
If this does not solve the problem replace the thermostat.