Your IP will change now and then but not often, you can get the STB IP adrress from the STB itself if you get stuck.
If you have cloned the information in (and remembered to enter it, lets face it, its the simple things we forget) and te connection isn't working I can suggest 2 things, a full reset of the router and start again or check your cables, I need a cross over from STB to Router and then a standard patch cable from the Router to PC. Double check your cable types to rule that out before we start looking to deeply into it
