Unplug the unit from power. Most all units have a reset switch riightr next to the power wire connection. push it in and it locks in. The photo cell can get dirty or dicconnected. If your power wire is good ( plug in something else and make sure) and you plug in the unit and it makes no clicks or sounds of any kind, then you need to open in up and cheak connections. The panel door that the power wire and the therostate goes intocomes off wqith two 5/16 headed screws, with the cover off check to see that all the wires are connected by removeing them one at a time and reconnecting them one at a time don't get them mixed up. On the back side of the panel that you removed there is the conplete wiring diaa gram. If it's not you don't have the right panel off. One reconnecting the wires read the wiring diagam and find the reset even if its automatic it still has one. cheak the connections here ( remove and reconnect ). The power wire it'self connects up and it's connections go bad most often, and the plug the plugs into your extention cord and the cord it's self and the plug that it plugs into being dead

Yes check all fuses, Also check for any resettable breakers on the unit. If that doesnt work check for ignitor issues Hold the ignite button for 20 seconds or so with the therostat avtivated to a temp that will turn heater on for sure, also check to make sure that there is fuel coming out and that there isnt air in the fuel lines

sometimes a good shake will loosen up some small air pockets