Does the power tilt switch work at the engine?
Can you jump the starter solinoid to crank the engine?
Have to cleaned the battery connections and made them tight? A loose connection will allow you to measure 12v at the starter, but it will not carry enough current to operate the starter or power tilt.
Measure the voltage at the starter solinoid when you try to start it. Does the voltage go away or does it stay?
If you can jump the solinoid to crank, and your battery and connections are good, you probably have an issue in the wiring harness anywhere from the connector on the engine to the helm. Most likely place for a break would be where it comes out of the engine.
Mike