there is a panic button in the initial favorites page 4 which you can program to whichever favorite page you prefer for that very purpose, but there could be a hundred reasons in your setup to cause it.

with the 7k in its initial state there should be no problem just playing back midis through usb. I can't predict anything without seeing the settings you have in whichever pc program you are using but would suggest, initialise the 7k midi, only enable one driver for playback only in the pc, disable midi through in the pc, try a midi preset in the 7k - sequencer in to 7k as slave without apc - but most probably there is a setting in your pc playback program causing it.