Nat?

192.168.1.254 or 192.168.1.1 on ur computer login username should be admin and password should be key on ur internet modem box once your in go to advanced settings and look for either DMZ mode and enable or UPNP those should fix ur nat settings to open and if not disable the firewall security on that same settings page and if that does not help u will need to open ports/pinholes the xbox ports could be found here support.xbox.com/.../network-ports-used-xbox-live

It's weird because last night it worked great?

if ur nats set to open it should work with no flaws if its moderate or strict please follow the directions in the post above.. if you are still experiencing technical difficulties please contact your isp so they can correct this issue on there side

something you can try that works for me...turn off your xbox...restart your modem and router and when it comes back up mine is always back to open.  Mine for some reason only drops to strict to moderate if my power goes out for some weird reason.