I'm the new guy, but have a bunch of experience with my home network, as well as converting to Apple product use in Ot. of last year. Can't handle Micro$oft any longer.
In your router page, how many devices are allowed to use your router all at the same time? I have a Linksys EA3500 N750 router and can carry an unlimited amount of devices at any time. My router page is accessible from 18.104.22.168 in a browser window.
Considering that you have not listed your router make and model, or whether your iPad has been accessible in the past or whether you have just purchased it and are setting it up, suggestions are generic at best.
In your iPad Wi-Fi Preferences panel, click the small blue arrow to the right of the network you use. In the new window, "Forget this Network." Hard reset the device (Hold Home and Power button till the device resets, about ten seconds.) After the reboot, go back to Wi-Fi settings and add the network you prefer. You will need the SSID and key.
This may not be a solution, but you haven't stated whether you have tried this or not.
Considering that you have a protected network, you know how to access the router page.
I hope this helps,