Try using the new computer to run non-gaming things, such as watching Youtube videos and some productivity tasks like using MS Office apps to create a document or spreadsheet. Does the computer perform all these non-gaming tasks without problems? Can you ensure that your Internet connection is working properly (Are you on an Ethernet connection or wireless?)? It does sound like an Xbox app problem, but I'm not familiar with that app. You can also try Googling the Internet for solutions to the problems you are experiencing.
As Albert Einstein said, "I could have done so much more with a Big Al's Computer!".