Some ethernet couplers are "crosswired" in order to implement the same function as using a "crossover" network cable to connect two computers directly. If your coupler is of this type, you will probably get a "Network Cable Unplugged" indication in the Laptop.
>>> Also there is a wireless router spare but my
>>> problem is I cannot connect it up as it has a
>>> DSL port. Is there a ethernet-dsl adapter?
If it is a combined "Router & ADSL Modem", its WAN port will be an RJ11 one for connection by modem cable to the phone line. You *cannot* convert this to operate as an ethernet port by connecting an adapter to it. You *MAY* be able to use the router as a basic Network Switch and/or Wireless Access Point by disabling its DHCP server (so it doesn't allocate IP addresses) and by connecting the incoming ethernet cable, your Laptop and the Xbox all to its LAN ports. When doing this, it *WON'T* function as a router, your main router still needs to perform the routing function to the various IP addresses.