When I came home today my heater was off and I cannot get it to turn back on. I have read the user's manual and I followed the directions to restart it (I have tried it 2 times) but it is still not lighting, it does not do anything. I checked the thermostat and it seems to be fine.

Do you have any suggestions?

Not enough information to start to guess. Age, Brang efficiency, standing pilot? Does it make any noises when you turn it on? See sticky post on top of main HVAC page for additional help.