By turn-over do you really mean turn over, I.E. the engine parts move ( flywheel "turns over") or do you mean the engine won't start up when you turn it over?
If it won't turn over then your engine is seized and needs t either be rebuilt or replaced.
If it won't start then you need to figure out which of the "big three" isn't happening
- Air - Carburetor and air filter clean, compression OK;
- Spark - You've already checked this and it appears to be OK; and
- Fuel - fresh gas, fuel line clear, spark plug will look wet, you can also smell it.
If you let the engine sit for months with fuel in it that wasn't stabilized then the carburetor is probably gummed up and needs to either be cleaned or rebuilt. Some people have reported success with the carburetor cleaning solutions that you dump in the gas tank. Others have taken the carburetor apart, soaked it in cleaner and then reassembled it, sometimes with new parts, sometimes with the original parts.
I would guess the carburetor needs cleaning. End of season maintenance is the thing most people don't do, they just put the OPE away and expect it to work months later.
Good luck.