This doesn't sound like an iPad problem. It sounds like a router or modem problem.
P.S. changing your password can cause more problems than it solves. If you change the password in the store, it doesn't change the password on file in 'settings' on the iPad.
It's not a problem for my modem because i solved my problem. I just turn off the wifi in my iPad and turn off my iPad too and is solved. My password of my modem doesn't change.
Thanks for your fast answer.