DNS Registration Failed

Hi you all...I'm new in this forum and this's my first message.
I'm from Italy and I'm 20yo.

I've got a boring problem with a brand new dell inspiron 6400 notebook.

I tried to plug it to a router (Us Robotics 9107) with two different configurations: 1 - static IP (DHCP off); 2 - dinamic IP (DHCP on) with the not-crossed ethernet wire.

in case 1 i can access the internet connection (from the router) but i can't share the pc contents because i can't see the dell on the net. if i try to refresh the lan connection an alert message pops up saying: "Impossible to complete the following action: DNS registration".
however, with the "ping" command from the promt i can see all the devices on the net (router, notebook dell, notebook toshiba and desktop) but i can't access their contents using the lan.

in case 2 i can't access the internet and i can't see the other pc on the lan, even using the "ping" command. it looks like beeing out of the net.

finally i tried to link only the notebook dell and the notebook toshiba using a crossed wire. but the dell gives me the same problem about "DNS Registration".

at last i think the problem is "DNS Registration".

Guys I'm getting mad trying to fix this bastard problem....please help me!

Thanks for answering !

thanks for your reply, man.

I already did it! but it still doesn't work!

I wait other advices...