I don't know if or how the original poster fixed his problem, but I found this thread helpful when my B2920 wouldn't start, so I'm posting with my experience.
The tractor is about 10 years old with just under 1000 hrs. It was running fine, when suddenly it wouldn't start. I heard a click and saw the dash lights come on when I switched it to "Run", the glow plug light came on at "Glow", but nothing happened when I switched to "Start".
I cleaned up the battery connections, although they looked in pretty good shape, and then it started for me. I then drove it to a more convenient spot than where it first died and shut it down. The next day (today) it wouldn't start, same symptoms as before.
After reading through this thread, I located the safety interlock switch on the speed control pedal. I wiggled the pedal a bit, and it started right up, so I think that was probably the problem. I'll add some lubrication where I think it might do some good, and if it continues acting up I'll follow my long-standing policy of disconnecting safety switches that interfere with operation of the equipment.