If your furnace is suddenly not running, you should check the pilot light to see if it's lit. This is located at the bottom of the furnace and is usually usually covered by a panel or box. It should be located near the gas valve. If it is off, first check the main gas line to verify that the gas is on in the house and turn the main valve to on if it has been shut off.
Next, check the furnace for specific instructions to relight your gas furnace. Some units have them directly on the furnace. If your furnace does, please follow the instructions located on the unit. If the furnace does not have instructions, then you should look for the electronic ignition button and a small red button near the ignition button. When you have located the red button, and press and hold the button down as you light the pilot light with the electronic ignition button on the furnace that sends an electric spark to light the pilot. Listen for the clicking noise as the ignition works to light the pilot. You should keep the button compressed for a minute or so after the pilot light is lit to allow the thermocoupler to heat up and THEN release the button.
Wait for ten minutes, to be sure that the pilot light remains lit. If it doesn't wait another 10 min and then try it again. If it still won't stay lit contact our office and we will send out someone to check the furnance.