Sounds simple, but have you tried rebooting your router?
If still doesn't work, post back with your Roku model number and router model number. You may have to login to your router admin settings to verify and change a couple of wireless settings for the Roku and your network to see each other again.
Roku Community Streaming Expert
Just another Roku user... I am not a Roku employee.
Insignia RokuTV, Ultra 4660x, Premiere+ 3921, Express 4k+ 3941