Hello Stratcat,
I'm guessing that 1 of 3 things has happened. Either the contrast has accidentally been turned down, the TranzPort isn't in 'Native' mode, or what's more likely, the midi port settings have changed in Sonar.
You can confirm the contrast thing really easy by simply pressing the battery button. If the battery level displays ok then the contrast isn't the problem. And click on the TranzPort icon to confirm it's in 'Native' mode.
What we see a lot with Sonar specifically is that the MIDI port settings in the SOnar/Options/Control Surface setup get changed really easily if you ever launch Sonar before all of your MIDI devices are turned On or connected. Sonar just reassigns things on its own.
Check these things out and let us know what you find.
CS