Did this, by any chance, happen just after an update on the tablet? If so, I would suggest (if possible) that you uninstall the update and see if the problem is resolved.
Also, it is possible that the WiFi networks in your area were closed, removed, changed, etc. so you are no longer able to detect them. Now if you are talking open public WiFi networks or your own modem/router, then that is different.
If this is your own modem/router, I would suggest restarting the it and then restart your tablet, ones your modem/router is completely restarted. This may resolve the problem.
Also, on your tablet, make sure your date and time are correct. Go to the "Settings" menu and then tap "Date & Time",. In here make sure "Automatic Date & Time" and "Automatic Time Zone" (if available) are checked. If there is a discrepancy between your device's date and time and that of the router, the connection may not work.
Another option to try is going into "Settings" then tap "Connections". Now choose "WiFi" and then "Advanced". In here turn OFF "Passpoint".