Try this

Get a helper

Have them turn on the headlights then observe the lights as the key is turned
If they dim a lot, you have a depleted battery (voltage high enough to run lights which do not draw much current compared to the starter, but not enough current to turn the starter which then draws down the voltage so the lights almost go out.

If the lights go out, you have a bad connection probably at the battery terminals but do not pass up checking ANY high amp connection.

If the lights do not dim, either the starter is bad, there is a bad connection in the starter hi-amp ckt, or the control ckt is not operating.

Old time diagnostic that points you in the right direction.