I'm sure it is not the motor. If the motor had burned out or blew, it would have had a lot of smoke and your circuit breaker likely would have tripped. I remember when my grandmother's Electrolux blew, it looked like a bomb went off! The smell was nauseating.
The sparks and the vacuum not working are not related. All old vacuums, and old electric motors in general, will make sparks from the armature because the gaps between the commutator and the carbon brushes is wide from age and use. Replacing the carbon brushes can help alleviate the problem. If the sparks are huge and like, shooting out of the side or something or burning the wiring inside, that is an issue.
It also could be that the vacuum was used heavily enough to wear the carbon brushes down to nothing and the vacuum cannot make a good electrical contact anymore to engage the motor.
But maybe I just have dumb luck, but 90% of all "Kirby won't turn on" issues I have found are the brushroll nozzle not being seated properly to trip the safety switch, or the safety switch is stuck and/or dirty. It's happened to 3 of the Kirbys I have bought that the seller said was not working. Sounds silly, but it does happen.
Next I would inspect the power cord for any damage, feel for any breaks where the sheathing feels like it is sunken in or kinked, could be broken wires inside the cord. Also check the socket connections at the end of the cord. You can try rubbing alcohol on a q-tip and sticking it inside and twirling it around to clean the holes on the cord. Very common for lint and carbon to build up in there and make a poor connection.
Check the socket prongs on the vacuum and make sure they are not loose or damaged as well.
It is possible that the tension from the new belt is lifting the nozzle up off the vacuum because of how tight it is gripping the shaft and might be losing connection with the safety switch, or you didn;t re-seat the nozzle properly when putting it back on.
The light bulb, I would not worry about. The vacuum has likely been banged around a lot from the donation box to being loaded on a truck, and then into another truck, and then into a bin, and then into the store, and so on. The little filament was probably fractured and you turning it on in the store was its last bit of life before it snapped.
That's my best guesses at what could be wrong, it's a starting point at least. I actually do have a 1CR but I haven't touched it in about 7 or 8 years. It will be getting its overdue TLC and be back up to spic and span shape hopefully this year.
