Are you getting atomisation of the fuel chug? There could be many reasons why it wont start. Dampness on the HT cables, corrosion between one or both electrodes and the blast tube shorting out the arc, crud on the sintered filter on the back of the nozzle (I get that a few times a year with the pool boiler), clogged filter in the oil pump itself, degraded rubber components as Dick says.
You need to be methodical when trouble shooting.
Is motor turning?
Is fan and pump turning?
Is fuel available at the bleed port?
Is fuel coming out of the nozzle? If so, is it a fine mist (good) or more of a jet (bad)
Is there an arc at the electrodes?
If so, is it being projected forward in front of the nozzle by the air flow or just a small intense arc that is nowhere near the fuel mist?