I am assuming you are connecting to a WiFi access point, and not wired. If you go into the Settings menu, under System/Advanced system settings, you will find Network Connection Reset. This wipes all stored WiFi settings, including passwords. Then try to connect it again.
One other potential issue is if your wireless changed its 5 GHz channel (this can happen when they are set to Auto-select) to one in the DFS range. Roku players will not work on those certain channels, but in theory it should just connect to your 2.4 GHz radio instead.
Dan
Roku Stick (3600), Ultra (4640), Ultra (4670), Ultra (4800), Premiere (3920), Insignia 720p Roku TV, Sharp 4K Roku TV, Nvidia Shield, Windows 10 Pro x64 running Serviio and Plex on a wired Gigabit network.