It's an oil burner so the red button is the primary control re-set. Could be any one of many things. Plugged filter, oil line, pump strainer, nozzle
Bad electrodes, transformer
Bad oil pump, motor, pump coupling
Bad primary control, cad cell eye, electrical issue and the list goes on and on. Call an oil burner tech.
If it starts and there's no flame, best guess is bad nozzle. If it starts, has flame and then it shuts down best guess is dirty cad cell eye or bad primary control.
At any rate, anything that gets done will require a combustion test after the unit is repaired to verify the cleanliness of the flame. Sooty fires plug heat exchangers and make a mess of your basement.