The use of the word 'spark' is probably making most people picture the engine cranking over but not starting because of problems with the ignition system.

But I guess in your case the issue is that the engine won't crank?

I'm probably repeating previous advice.

1) Turn the lights on, and see if they dim or go out when you try to start it. A weak battery (and modern batteries seem to go from good to weak much more quickly than they used to) or bad connections at the battery can power lights just fine, but when under the load of the starter just fizzle.

2) On a manual car, a wire runs from the ignition switch to the starter, when you twist it to the start position it sends current to the starter solenoid. On an automatic, for whatever reason, they don't want you cranking the motor unless it is in Park or Neutral. So the wire goes to the transmission to the neutral switch, which only passes the current along to the start when it is in one of the particular gears (P, N). The adjustment can go out on the switch, wires could fall off it, contacts could fizzle.

3) Once you actually get 12 volts to the starter solenoid,what you are actually doing is not powering the starter motor directly. because that's a lot of current and you'd need huge wires running all over, and the starter switch would need to be huge. You are actually powering the starter solenoid, which is a sort of big gnarly relay built onto the starter. When powered it snaps closed, both closing a heavy set of contacts and pulling the starter gear into mesh with the flywheel. The solenoid can fail, failing to pull closed when energized. And the contacts can fail, refusing to pass electricity through them to power the starter motor.

First thing I'd do is get a multimeter and check to see if you are getting 12V to the little wire on the starter when you twist the ignition key to start. If so, heavy suspicion is cast to the starter. If not, work backwards to the neutral switch, then back to the ignition switch.
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'63 PV544 rat rod, '93 Classic 245 + turbo