It seems you have a real problem. A starting circuit should be so simple. When you turn on the ignition, it powers up the ignition circuits and when you turn it one step further, it sends 12 volts down to the solenoid which activates the starter.
To diagnose where the problem is, you need a meter and might also have to do some surgery. With a meter capable of measuring 12 VDC, place the negative on a body or engine part and hold the positive to the input (a thinner) cable of the solenoid. Then have an assistant turn the key to the start position.
Voltage? Yes means the solenoid is faulty. No means that the supply from the switch is missing. This may be the actual supply to the ignition switch (a fuse) or if this is ok, the actual switch itself. The surgery involves accessing the switch, identifying which cables are the 1) supply in, 2) auxiliary out, 3) ignition out, 4) starter. This can be ultra fiddly since you need to take off the plastic housing around the steering column when you will be confronted by a mass of wires going to lights, hooter, wiper, etc
An ignition switch consists of 2 parts. The cylinder into which you insert the key and underneath, a plastic part which contains the switching components
As with all faults, car, fridge or wife, try the simple things first before going for an open heart op
