[Darryl Ramm]

^^^ what Sardi said.

Just to be clear MIDI has nothing to do with getting audio from your synth. MIDI connections in Audio/MIDI setup are irrelevant.

The USB interface may or may not be totally irrelevant... often the synth/keyboard is only providing MIDI over USB... *IF* (big if) it is also providing audio over USB then you need to get that connected to Pro Tools and that is controlled in the Pro Tools Play Back Engine settings, possibly also requiring you aggregate that input from that Synth with the audio device providing sound output ... done in the Audio part of Audio/MIDI setup.

But for most setups audio does not cone via a keyboard USB connection, more often audio gets to the DAW via analog outputs of the synth going into analog inputs on your interface, possibly line level analog or into a preamp using a DI box or DI input in the preamp or interface. Oh and alright just for completeness some synths/keyboards might provide digital output like S/PDIF so you could use that to get to your audio interface.

You will get better help here if you just say exactly what synth/keyboard and audio interfaces you have.

And the track you record this audio to needs to be an *audio* track, not an instrument track. That is a common cause of problems.