TG582N - Cannot Access Internet

[#1]

Hi,
Have just swapped to a TG582N and having problems that cannot seem to overcome.
First all lights are green on the box indicating everything is good - internet, wifi etc etc.
Second I cannot access the internet from a laptop over wifi unless I "assign the public IP address of a connection to a LAN device" ie the laptop. I have tried another laptop, tablets and smart phones but all have the same problem. All devices are picking up an IP address and can access the admin pages of the modem router. The "Home Network" page on the router shows all devices connected. I have not tried a direct ethernet connection as of this minute, but will do so.
Third I have another computer connected by ethernet that I use to access via XP Remote Desktop but cannot connect to it from within the LAN. This maybe related to point 2  I guess.
I have a linksys WAG160N which I can use and is fine but want to use TG582N as it seems to get better speeds. All and any help gratefully received.

[#2]

Another thing worth mentioning is that I have switched off the router's firewall but still no good. Also cannot ping my remote desktop either.

[#3]

Have you tried doing a hard reset of the router?

[#4]

Ok did that and it worked - thanks for the suggestion!
When I was reconfiguring the router I noticed it stopped working again if I changed the IP address from the default! Not sure why but means I have to sort out all the other machines to match now!! Never mind! 

[#5]

I would imagine you need to change the gateway/DHCP settings if you change the router IP address too.

[#6]

Hi honestsam,
I've posted a graph of your connectivity, it's showing constant connections then disconnection and that these are being actioned from your router?
<img src="http://ccgi.psmith12.plus.com/visradius/generated/image13642179153356.png"/>