I have seen this once and a while. Firstly check the power button is not "wedged" or something to cause intermittent contact. Then remove head united and inspect/clean contacts. Also remove the powerpack and re-install. If that didn't work, I would open the motor cover and re-seat the connectors. I hope your up and running!
Suggest dropping by your local Bosch certified shop and have them hook up the bike and get you a diagnostics report. Can indeed be a button which can be tested in a few seconds with the software or may need a software update.
Another suggestion is to make sure the contacts on the rear of the display and mount are clean.