Have you tried forgetting the info, turn off the tablet's WiFi, restart(turning off and back on) the tablet, turn on the WiFi settings and then reenter the info. Be sure that you have the correct WiFi connection you are trying to access and turn on the option to see the password as you type it. That should help.
Now if that doesn't work, try your tablet on another WiFi and see if it will connect. If it does, then I would start to wonder if the WiFi you have is limited in the number of devices it will let you connect. Some carrier's/service provider's do put limitations.