This is not uncommon. There are several things to try. Not necessarily in this order.
Stand right next to the router.
Clear all WiFi setting on your tablet and try again, making sure you have the correct WiFi password.
Make sure your tablet has the same encryption settings as your router. (Best is WPA2)
Change the WiFi channel and set it to a fixed channel rather than auto select.
Temporarily disable encryption on the router and connect. Then reset the encryption.
Change the SSID and reconnect then change it back.
Turn on the guest network on your router, if it has one, and try that. If the guest network is already on, turn it off.