The power went off and when it came back on, the heater will not come on. I replaced the batteries in the thermostat and it clicks when I turn it on but nothing comes on. Any idea? I checked the breaker box and breaker to heater is on,

Could be a defective circuit breaker, loose connection in the circuit, etc.

If you do not have the knowledge and equipment to work on wiring, need to call in an electrician to troubleshoot the problem.

I agree with TK but think you really need an HVAC repairman. Today's furnaces and tstats are more like computers and need a technician. Many furnaces will trip limiter switches if power has been killed while the furnace was firing.