My denon avr-1906 amp will

Question

my denon avr-1906 amp will not turn on correctly. When the standby button is pressed the indication surrounding the button flashes green but when you hear the relay click in for presumably the power amp, it powers down and the indication returns to red surrounding the standby button. The manuals hints and tips say that the vents could be blocked or its over heating, the vents are clean and the unit is cold so I'm at a loss as to what to do next?