I just installed this (it is hardwired to a motorola nvg510) and it works fine. when I disconnect the ethernet wire I get nothing out of it. how do I set this up so I can put in another room and use i

I bought a used deco m5 system which I get tomorrow. I am getting a brand new router on Wed. to replace my old router. Is it ok to set the deco up tomorrow even though I will be replacing the current