ok.  bear with me.  this is a bit tough to troubleshoot with text.
are you using a simple instrument track for the tts? 
bring up preferences/midi/devices - make sure the mpk is checked in input devices (there should be 2 entries for it - check them both).  make sure the midi out for the mpk is also checked and the microsoft gs wavetable synth is not.

Okay, not sure how it got unchecked but it's checked now I do seem to have live play output. Pardon me if I seem dubious, but I'm sure it was checked before and still had intermittent output... I'll play with it now and see how it goes. Thanks!

tindog13
 I've been watching as many YT videos about Midi, but they tend to start at a higher level than where I'm at... any help would keep me from jumping out my window.

Have you watched this video? Aptly named "MIDI for beginners", that may well help with understanding the general set up etc.

tindog13
Okay, not sure how it got unchecked but it's checked now I do seem to have live play output. Pardon me if I seem dubious, but I'm sure it was checked before and still had intermittent output... I'll play with it now and see how it goes. Thanks!

This can happen sometimes if you change usb ports. windows can be fun!

Thanks, I'll give it a look.

Well, great video ("MIDI for beginners"), but while it all seems pretty straight forward... choose this, select this, click this, choose sound, and Voilà - sound. But it doesn't cover if you... choose this, select this, click this, choose sound, and Voilà - nada. The problem I'm having now... problems... is that it is inconsistent... I have a new project going, it's not crashing anymore, but I can only hear my chosen instrument when the track is running, usually... sometimes I get sound when it's static but not reliably or permanently... no sound, hit play (or record)... then I get sound. Hit stop, no sound. Then, often notes will start sounding and I can't stop them until I stop the track (which also happens on playback sometimes). And something that I can't find is randomly triggering the "patterns" on the low end of the keyboard in the SessionDrummer3 patch. Still struggling with drums sounding simultaneously with other sounds, whether echo is on or off. Tried buffer sizes. Also, fighting latency.

In fairness it does cover a couple of instances where there's nada.... I never edited the mistakes and wrong selections out as I thought it served a purpose of how easy it is to get nada.
 
If you are getting nothing when the transport isn't running it sounds like the audio engine is stopping. You can turn that on in the transport bar (bottom left icon in the transport display) or if you check "Always stream audio through FX", in Prefs-->Audio--->Playback & Recording it will help stop it turning off in the first place.

As you can see, I continued to edit that last post as the manifold recurring issues came to mind. I checked the Audio Engine and it is on, but even if I turn it off it comes on again as soon as I hit play and doesn't go off when I hit stop. And the "always stream audio through FX" was checked.
 
I am trying to follow the video step by step, but there are differences that make it difficult... as a for instance, when the TTS-1 is added and the OK button is selected, in the video the TTS-1 panel comes right up on its own... that doesn't happen for me, not a big deal as I can just go double click the icon and it comes up, but took a bit to figure that out. Also, when the output is changed the pull down menu offers Cakewalk TTS-1... mine doesn't. It offers; master, metronome, preview, reverb, drums, parallel compression, toms, cymbals and percussion. As a rule, my output seems to always have to be set to "Master" to get any sound.
 
Right now, I have instruments selected... echoes on, if I open the TTS-1 panel and hit preview I can hear the sounds, but not when pressing keys on the MPK261.
 
As another, for instance... I thought I had it right... input set to MPK261 Omni, output to Master, banks and patches set to Piano 1 and I was actually playing the piano patch from the keyboard. Then it just went away, now, silence. Moving through settings, trying to get it back.

Okay, what is never said in the video, until it gets to the point where the output wasn't set, is that there has to be an audio track... I wasn't getting that. Does that mean an audio track for each midi track, or is it one audio track open for the project?

Sounds like you are using a Simple Instrument Track. I purposely used a separate MIDI and Audio track to demo the routing that is hidden by a SIT.
 
Try setting the option to have separate tracks when you first load TTS-1. That is also where you find the option to have TTS-1 interface open on loading. There's a checkbox there for it.
 
To select TTS-1 as an output you must have a MIDI track. The sequence is
 
(Keyboard or MIDI clip)----->MIDI TRACK INPUT-------->MIDI TRACK OUTPUT------>TTS 1------->AUDIO TRACK INPUT----->MASTER BUSS.
 
A Simple Instrument Track (SIT) cuts out much of the routing so you simply set an input and output straight to your master buss (or other downstream buss)