Failing that, it's probably Windows being a pain.

Do this (bits in red are specific to your router, but the ones I put are very common):
  • Click start
  • Click run
  • Type "ncpa.cpl" and press Ok
  • Right click local area connection and go to properties
  • Double click "Internet Protocol TCP/IP"
  • Switch the top dot over to "Use the following IP address"
  • IP address: 192.168.1.64
  • Subnet mask: 255.255.255.0 (Will probably appear automatically)
  • Default gateway: 192.168.1.1
  • You also need to specify DNS servers, so grab them from your ISP or find some good ones online
  • Done