iPad can't go online even though it can sense wifi signals

If you are having WiFi problems it is necessary to isolate whether the problem is with your network or your iPad. Note: Do NOT consider your network to be blameless if some other devices can connect to it.

First, test your iPad on some other WiFi networks: a friends, Starbucks, Barnes & Noble, etc.

If it works well there then the problem is probably with your network. Try restarting your WiFi router by removing power for 30 seconds. If that does not help check for a firmware update for your router. If none exists which corrects the problem consider replacing the router.

If your iPad does not function well on other networks it possibly has a hardware problem. You could try Settings > General > Reset > Reset Network Settings to see if that corrects the problem. If not, contact Apple Support or visit an Apple store for evaluation. They can provide a replacement if your iPad is bad.

If you need more help please give the make, model, and version of your WiFi router and how you have it configured.

See also here: http://www.apple.com/support/ipad/wifi/

It could be an iPad problem or a router problem. Try your iPad on some other networks to see what happens.