1) set up a router with the cube and PC ONLY on the shared connection, no connection to actual internet.
1-A) change the subnet mask if it's not in a range the cube will take then let the router restart ONLY if the subnet is not already in the right range ie 192.168.1.(devices)
2) go in to the router settings and read off what IP is assigned to the cube.
3) Port 80 or 8080 is the port for HTTP connections on MOST working cubes ( no need to add it if you use a browser to connect to that IP )
4) on the PC, open a browser and point to the cube's IP ( try with out port first ) and see if you get any error. 404 is not good, worse if it's a 500 error ( 500 range is basicaly you are not allowed in )
5) ASSUME you got in by this step then try temporarily setting worker and pool.
6) still with no internet connected to the router reboot the cube and re-check the settings, if it's working properly, the worker/pool would have been saved and errors on no connection. If this is the case, connect to the net.
As a personal note, I have modem to router to router to miners so that the home PCs connect to the first router ( wifi and wired ) and all the miners are on the same subnet ( different from the home systems ) to prevent a few issues with the DMZ ( to miners ) and firewall settings for some online games.
If this helps, feel free to test with mining for an hour for me
stratum.btcguild.com:3333 worker nybbler905_2:TYforMining4Me 
