Welcome to the forum!
The standby light will start blinking if the protection circuit is activated. That could certainly be caused by turning the volume up loud, and it will also depend on how much ventilation you have around the receiver and what speakers you have connected to it. This can also be caused if copper strands from your speaker wires are bridging the gap between the two terminals and causing a short circuit.
From page 31 of the Onkyo owner's manual, here is the recommended procedure to clear that issue:
The STANDBY indicator is flashing
The amp protection circuit has been activated. Remove
the power cord from the wall outlet immediately.
Disconnect all speaker cables and input sources, and
leave the receiver with its power cord disconnected for 1
hour. After that, reconnect the power cord and press the
[ON/STANDBY] button again. If you can not resolve
the problem, contact your Onkyo dealer.
I'd say it's worth following that procedure to be sure. When you reconnect your speakers, make sure that you don't have any copper strands bridging between two terminals (on the receiver and on the speakers themselves).
Btw, what speakers are you using?
