Welcome to TRS
So when you turn on the key do the dash lights all come on?
Is it a Manual or Automatic transmission?
Each has a different kind of switch to disable accidental starting "in gear", so if switch is not "Closed" starter motor will not work.
There is a 50amp fuse in engine fuse box that powers the ignition switch, maybe Fuse #5 but not sure on the number.
And in the Cab fuse box fuse #24, 7.5amp, powers the starter motor relay, but from power coming from the 50amp fuse.
So check that 50amp fuse, it powers radio and turn signals.
You checked the battery cables, I assume, but did you check BOTH ENDS of each cable.
Follow the larger Negative cable to the engine, and make sure connection is clean and tight.
Does the key feel loose or very tight, hard to turn?
The actual ignition switch is under the steering column above the brake pedal.
The Key pushes and pulls on a long rod when it is rotated, this rod is attached to the ignition switch, which is a slider type switch.
The rod slides the ignition switch into its various positions, ACC, OFF, RUN, START
If ignition switch isn't moving as it should then no power to some systems