Howdy
Need some more info.
Is this a new to you boat?
Turn the key to start and starter will not engage and crank?
Can jump the starter at solenoid but still will not start?
If above is correct them may have 2 issues.
See if there is 12V at the coil pos post when key is turned ON
If no 12V then may be the kill switch
Is the slave relay clicking when key is turned to start?
If not then may be the neutral safety switch