How about starting with all the models of the the Roku devices you have and your Router model.
Either all your Rokus broke and died, or you are having a network issue. I am hedging my bets on the network unless you have some very old Rokus.
You are going to have to login into your router's admin panel to fix any network issues. Post back with the settings from your Wireless Settings (within router) if you can, and the above info mentioned above.
Also, if you can for testing purposes, see if you can connect the troubled Rokus to hotspot to get a connection.