RunningMan: It appears as though you are currently doing double NAT. EDIT: @sbiddle beat me to it
What happens if you bypass your router, and plug your computer directly in to the modem? Does it pick up the DNS servers OK then?
If this works OK, what IP address is being given to your computer? Is it the public IP address given by your ISP, or a private one (192.168.x.x)? Trying to work out if you have the AM300 in half bridge mode...
I suppose it is not an ideal setup. I originally was using the AM300 only in wired fashion with the switch but then bought the Netgear WNDR3700 to support my wifi devices and found it wasnt also an ADSL modem (this was like 4 years ago) but then after setting it up like this it has been rock solid for me for 4+yrs.
I have the AM300 plugged into the Uplink of a switch and the Netgear WNDR3700 also plugged into that switch along with ethernet cables going to multiple rooms in the house. They are in a closet under the stairs, so would just removing the Netgear from the switch and changing AM300 operation mode from gateway to Router do the trick? (obviously that kills wifi access, but is that considered direct even though there's a swtich in between?
Not sure why it would go pear-shaped all of a sudden though...
I'm in a new-ish neighborhood and when I first moved in 4yrs ago, they said it was a 1+yr waiting list for broadband since all the ports in my exchange were full. Eventually within a few weeks I called Chorus out and was able to appeal to the guy who was soo helpful, and despite weeks of Telecom saying it would be minimum a year to get broadband - or someone in my neighborhood would have to die to give up their port - this Chorus guy pulled some strings or something I assume because magically after appealing to him there was a Chorus van outside our exchange installing new equipment and I was able to get broadband in a couple of days from talking to him directly.
Mentioning that is all probably a red herring since my setup has been working fine since then, but I'm wondering if there is anything with my exchange at all.