You need to check your computer isn't setup to ask for a certain IP, this can be done:

Right-click My Network Places > Properties > *The network connection your using to connect* > Right-click it and go properties > In the box double-click "Internet Protocal (TCP/IP) > Make sure it's set to "Obtain an IP Address automatically".

Else it's probably a setting in your router, I'd need to look at the router control panel to see what it could be, however it could be a fault with the user settings for your router connecting to your ISP.