It is likely that the preamp injected DC into the amp when it started. The amp would then go into protection mod. Unless you unplug the mains cord and wait 30 seconds, it will not re-start immediately after such a protection incident.
This design is intended to protect your speakers, should such a thing happen.
If, after you unplug the power cord, plug it back in and attempt to re-start the amp, it is still unresponsive, then please by all means, call us.
Sincerely,
Dan W.