I'm seriously really pissed right now, I was supposed to have a xbox360 LAN-party tomorrow, because of that my best friend already came to help and just hang-out. Normally I use the wireless network adapter, but since I only have one (and my friend uses wired at home) we had to connect his 360 with a Ethernet cable (the plan was to connect all the 360's through ethernet). We thought this wouldn't cause a problem unlike the wireless connection, but after connecting xbox-live isn't working. The problem is the 360 can't seems to get an IP-address from my gateway (modem and router in one). This while DHCP is enabled on the gateway.

What I've tried already:using a static IP power cycling the gateway (so leasing shouldn't be the problem, but maybe it can still be?)

I do not know what else I can do. Oh and I also have a PC connected with ethernet and that isn't causing any trouble ( and connecthing my laptop isn't either).

I really do not want to cancel the lan-party, so if anyone knows a lot about networks and in particular DHCP problems help would be really appreciated.

Sorry cannot help but I will bump to see if anyone else can. Good luck to ya

try to unplug the pc and then power cycle the modem. See if the 2nd xbox pulls the pc's address. Also, what is the range of ips configured on the router.
DHCP Start Address, DHCP End Address, subnet mask, gateway and any exclusions?

Edit: You should plug the xbox into the same port as the pc and with the same cable. 

i don't know what are network settings in the x360 control panel but in general when DHCP gives you troubles you could use a static IP address (not duplicate of already used addresses and in the same subnet of the gateway).

Mind that when you use static addressing you have to provide the device (x360 in this case) with additional info in order to connect it to the internet (this could be the reason you are experiencing troubles even using a static address): you have to set the default gateway with the IP address of the router (usually is the 1st usable adress in the subnet) and you need a DNS IP address (you can use the same adress you use for your PC..from windows click on start->run-> write "cmd" -> from the command prompt issue "ipconfig /all" (mind the space) and look for "server DNS" in the output )

hope this helps :)

Given that your PC pulls an IP address from the gateway with no trouble, my assumption is that the problem is the Xbox360. DHCP is an incredibly simple protocol and usually when something's not working properly it's a simple problem, and the fault isn't with DHCP.

Make sure it is configured to get its IP address from DHCP. Also, this may sound obvious, but don't forget to double check the cable connections, try plugging the xbox360 into a different port in your router (try the one the PC is using)

Check the range of IP addresses your router can give out, and it's current leases, perhaps it's exhausted. Increase the range if this is the case.

If all else fails, give your xbox a static configuration (copy the ip information off your pc, and just change the IP address) and see if that works. Although that's not likely

We had this same problem when my brother got back from abroad with a new laptop on our network. We couldn't get either of them online at the same time. You are probably going to have to put in the IP address of your router manually into your Xbox.
When you do a connection test does it say IP failed?

Thanks for are the help, but I already have done everything described in this thread, I going to make at least 2 of my friends take there router, hope that will help.

Why dont you just set the router to give out static IPs? and then manually assign an IP to your xbox in the range that your router is set up. If it works do the same to all the xboxes for the lan party...

So go in to your router and specify IP address range from 192.168.1.100 to 192.168.1.150 for example and then give out statics to xoxes and your PC...

Don't forget the routers static gateway and DNS...

Already done that, I know quite a lot about networks even wrote hacks for it (and I've done countless of  LAN-party's and always something is up with the network), I was just asking if somebody had an onther idea which I was missing.

Have you tried a different cable? I've seen computers not get DHCP because one of the 8 wires in the ethernet cable is damaged. Also look at the pins inside the X360 NIC to see if any of them are bent or damaged, do the same on your switch or router also. You may also try a different port on the router.

If this doesn't work, you may have an issue with the X360's NIC.