I have an armstrong ultra sx-80 gas furnace my problem is when I turn the unit on, the blower comes on but the burners don't light. The furnace was running fine when we went to sleep??

Should be a flashing diode on the control board. Count flashes and compare flashes to the code sheet, usually on the fan side cover. Could be any number of things from a blocked vent to a bad control board. Hopefully it is something easy, perhaps a hot surface ignitor.