As noted above, if a simple box reboot doesn't work, the next step is to reboot your modem, router and Roku in that order. Unplug all three, wait a few mins.,then plug the modem back in and let it boot up completely. Then do the same with the router, then the Roku.
No, I don't work for Roku.
Netflix Player N1000X, XDS 2100X (premature death by lightning)
Roku2 XD 3050X, Roku2 XS 3100R, Roku2 4210R