Shuts off then red light indicator flashes, disconnected all speakers but still wont work

There are a few things that could be causing this to happen. The first thing you should do is check all the speaker wires connected to see if they might be touching each other somewhere. What you are describing sounds like there might be a short. Also, is the receiver well ventilated? What is happening is that it is protecting itself but shutting off.The 590 is going in to Protection Mode due to some fault it perceives. The quick flashing red power light (as opposed to a slower flashing light) would indicate either speaker wires touching another terminal, driving 4 ohm speakers to loud, or amp failure.

Connect the 3.5mm cable to the iPod headphone output and the two RCA plugs into any unused analogue audio input on the Denon AVR 1803. Then choose the appropriate input on the Denon, press play and enjoy the music. Be careful about volume. Start with the volume on the iPad low and adjust to suit.
Cheers, Don.

Well on most models red ring singals :

1 ) speaker wires touching something they should not
2 ) internal overheating, shutting down to protect
3 ) something is wrong, bring in for service.

I'm guessing it's out of warranty?

Sounds like you could have a bad speaker connection. Try disconnecting the speakers and see if it stays on. If so, connect one at at a time until it goes off to determine which one.

as per your request: Denon AVR 1803 Manual

http://www.fnet.de/anleitung-Receiver-Denon-AVR-1803-43117.html

In most AV receivers if the standby light flashes after turning on and you don't hear the regular click of the relay engaging after 4 seconds, indicates an output short or amplifier failure. The protection circuit prevents any further damage by not turning on system.
You will need professional help to fix this problem because even to a electronic enthusiast the construction of a typical AVR is not service friendly.

A shorted wire would do it. Take it to a tech and tell him what happened. If you remember which channel you were handling at the time it might help hum to find the problem.

probably one of your speakers has blown.. disconnect them all. turn the reciever on.
if this works turn it off connect one speaker and turn it on.. keep going until it goes red...
when you find the speaker discennect all the other speakers keep this one connected and confirm that it is this speaker giving issues.

if the amp doesn't come on with all speakers disconnected, remove the visual outs and start it with nothing connected. isolate the issue if this works. otherwise it might be your amp.

check your speaker wires make sure none are touching each other this will cause a short and shut the reciever down

speaker terminal are short circuit,switch power off connect speaker properly then switch power back.
-the ventilation holes of the set are blocked-turn power off and make good ventilation around leave the set to cool and turn power back.
-the unit is operating at continuous high power turn it of and allow for cool down and switch it back.