Try the following...
1. Turn off your tablets "WiFi".
2. "Erase", "Remove" or "Forget" the log in information for your WiFi.
The above steps are reversed on some devices.
3. Restart the tablet.
4. Now try turning on the "WiFi" and and input the settings to your router/modem.
This should resolve the problem.
Note, if it keeps kicking you out when the tablet gets turn off and back on, then there may be a problem with the tablets settings, or you could have an app that is giving you the problem. If you have recently installed a new app, or updated one, you may wish to remove the app and/or the update to see if that resolves the issue.