I found the solution on some other forum. I had this problem 3 months ago and after days and hours searching the net i eventually sent it back to Denon to get it repaired as suggested by everyone who came across this bloody Network problem. Anyway after 50 days i eventually received my Denon avr3310 back. It was back to normal working order. It failed on me 10 days ago again and completely dispaired i was about to return it for the second time.
However a few hours before sending it back i decided to try my luck again on AVSforum and others when i found a new solution that i had never encountered before. I tried it and it worked like a charm. MY Denon AVR3310 NIC reset itself and worked again !!!! Couldn't believe it !! I'm stunned this hasn't become common knowledge considering how long this NIC issue has been unresolved.
anyway , sorry for the rambling....here it is..
"reset the network card by turning the receiver off the same way as before (small power button). Then, press the Up and Down buttons on the circular Up/Down/Right/Left set and turn it on, holding them in for about 5 seconds before releasing them. Once it's done resetting, go to Menu, Manual Setup, Networking and verify that it has an IP address"
look for post 14 from highfigh (Highfigh ...hero of the day !!)
Hope this works for you (did the trick for me)