79 silverado big ten no crank help

[Dnjsdad]

I recently acquired a one owner, 79 silverado with 109k. It ran flawlessly, my son turned the truck off, and when he went to restart it, it won't turn over. The starter is not engaging with the key. We tried jumping the starter, it turned over but still didn't engage the flywheel.

I'm thinking ignition, or solenoid but those are from my very very limited knowledge.

Thank you in advance for any help.