Cubase 6 won't play midi data

I have a dedicated music computer, offline, running on Windows 7. Recent trouble with both the boot C drive and the data D drive compelled me to clone the data from those drives onto new drives, which were then re-installed back into my old Windows 7 machine. I have an Mbox interface, several internal VSTs, and a Yamaha ES8 keyboard controller.
Cubase 6 launched just as before, and I opened a project (from before the drive issues), with audio and midi data, that I knew was trouble-free. The audio tracks played perfectly. The midi tracks don’t play at all, although the blue indicator between the track name and the track data lights up. A track set up to receive keyboard data also makes no sound when I play the keyboard. A track set up to receive midi data makes no sound, but if I open the VST player and plonk a key on the interface with the mouse, I do get sound.
What might my problem be?

Hi and welcome to the forum,

What is the Output of the MIDI Track(s)? Where are the MIDI data routed to? Do you use any virtual instrument (VSTi like HALion Sonic SE), or do you send the data out to any hardware synth?