Try this:
On the tablet in WiFi settings select your network and 'forget' the network.
Turn the tablet off.
Disconnect and power to the router for at least 30 seconds.
Reconnect the power and allow plenty of time for the router to fully reboot, 4-5 minutes.
Turn the tablet on and try reconnecting.
If no good, check the security settings. WPA2 works well with most devices and is very safe.