I typically use an USB audio interface (Roland Duo-Capture EX) along with MIDI keyboards for input.  X2 has been working well for a few months this way along with some VSTs.  Now I went and made a temporary change so I could use my computer audio plug and installed ASIO4ALL for the Conexant sound board.  (just so I could work with a VST while away from my keys.)
Upon reconnecting to my USB interface, I can't get my MIDI keys to respond after changing the Audio Device back to my Duo-Capture EX.
What have I missed?
(I just want to play music, not be a computer programmer.)

Could it be the ASIO restriction of one I/O driver is preventing SONAR from seeing the Duo-Capture Ex completely?

Sonar is using the Duo-Capture output because I can hear the soft synths thru it.  I can even see the meter jumping when I hit the MIDI keys, though they're not in sync.

Make sure it is enabled in Preferences under devices. If it is not listed there, try to hot-disconnect it and connect back and see if Sonar detects it. You can restart your computer and see if it detects, or make sure you set right inputs/outputs. If you can hear your plugin output, then it must be Input. Check preferences.

It is enabled in Preferences.  I even disabled (unchecked) the ASIO4ALL device/driver.