Your router may no longer be giving your iPad a valid IP address via DHCP. Go to Settings > Wifi > your network name and touch the ">" to the right to see the network details. If the IP address starts with 169 or is blank then your router didn't provide an IP address and you won't be able to access the Internet. If this is the case there will be nothing under router, DNS, or search domains. The 169.254.x.y IP address is self assigned by the iPad when it gets no IP address via DHCP from the router and is intended for ad hoc networks with no DHCP server.
Sometimes the fix can be as simple as restarting your router (remove power for 30 seconds and restart). This gets the DHCP daemon in the router running again. Next, reset network settings on your iPad (Settings > General > Reset > Reset network settings) and then attempt to connect. In other cases it might be necessary to update the router's firmware with the latest from the manufacturer's support web pages.
If you need more help please give more details on your network, i.e., your router make, model and version, the wifi security being used (WEP, WPA, WPA2), etc.