It happens to me when I use my wireless adaptor all I do is unplug the router for 30 seconds or so and plug it back in and it should work again

It is probably because your connection is not strong enough bro. if anything you should call the company that you got your router or modem from.but if you can tell me all of your info on about your router/modem then i can easily hep you out man. message me back so i can help.
-Brian

Honestly, I had this problem before and it was actually a piece inside my xbox that messed up. But, try to restart your router and or modem and let it stay off for a minute or two. Reset it and wait till all of the lights are completely on then turn your xbox on and try to sign in. If it doesn't let you. Try to go to your network connection and manually put in a ip. If you need help or walk through on all this. Please pm me.

ru Wired or wireless ? then if its wireless its sometime will like not cc

try reseting ur modem or router thats happen to me then i reset it and it waz fine

i have had this happen to me a couple time, i just reset my router and it works perfect

take out the power of both your modem and/or your router. i did that yesterday and it worked like a charm

Try clearing the cache on your xbox bro.

you have to reset your connection.. test the xbox.. then if it doesnt work again take out your eithernet.. restart your modem.. wait about 30 min.. try again.. if it does not work last resort is to call xbox and tell them your xbox is having a connection issue and they will walk you through.. please rep if this helped in any way

try disconnecting eveything and reconnecting, i had to