Troubleshooting

Is your thermostat set for heat?   Are the switches in their proper positions (heat, cool)? 

Is the set-point set above room temperature? Is the fan on auto?

Are your batteries good in your thermostat?

Is the furnace plugged in?  Is the power to the furnace turned on?   Is the fuse blown or the breaker tripped?

Is the furnace door properly closed?

Is the gas turned on?

If you don't have an automatic pilot lighter, is the pilot lit?    (Generally furnaces prior to 1986 do not have automatic pilot lighters.)

Is your filter clean?

Is there a reset button on your furnace? If there is, try pushing it.

Are all of your registers open?

To "reset" your furnace, unplug it for five minutes and then plug it back in.