Question : Cannot contact DHCP server!

Here's my problem.
I have a old computer (PI 166mhz with Win98) and it connects to the internet perfectly with my LCPET-3 cable modem.
Nothing goes wrong with it, it contacts the DHCP, get's an IP atribbuted fast, etc..etc..

Then I bought a AMD 1200 and fitted it with WinXP pro. The idea was to take the internet away from my old computer and set it up on my new one. But alas. It does not work.

In the new computer as I try to renew the IP adress it states that it cannot even contact the DHCP server, thus no IP adress given.

At first I thought it could be a problem with my Ethernet adaptor, so I ran out and bought another one, only to receive the same treatment.

Really could use some help, I am getting a little desperate. :/

Answer : Cannot contact DHCP server!

If it was a USB modem, ascension1014 might have been right.
However, as it is an ethernet modem, and is just a switching port, it registers the PC NIC MAC address, as EluSiV3 said.

My cable supplier (Telewest) uses an ethernet cable modem, and it registers the PC Mac address ( unique number for each network card) when set up, as I found out when I fitted a new Network card to my PC!

This is to stop you connecting lots of machines, (although a router, which has it`s own mac address, will allow this).

They allow you to register up to 4 Mac addresses via their website, or over the phone, but you can only connect one at a time.