There is no reboot button on this unit. To reboot the receiver, simply unplug AC power for 30 minutes, then while plugging back in press and hold the power button for 5-10 seconds at the same time to reset.
Check all the speaker wiring for shorts, make sure they're also not touching the chassis of the receiver, or are not otherwise pinched or frayed. If all looks well, try disconnecting all the speakers and cycle the power off, then on again.
Try connecting the speakers one at a time until one of them shuts the Audio down. Check this speaker with a multi-meter and make sure it is reading between 4-8 ohms.
If not, the speaker may be blown and is causing the receiver to short out and therefore power the audio down.
If you still cannot get any audio through the system, then it likely has bad output transistors, or capacitor and is in need of service.
Here is a link to the Operating Manual