First try using a wired connection, if possible. There are just fewer things that can go wrong w/ wire. If wire works, then at least you know the problem is related to wireless. And vice versa. If wire doesn’t work, then the problem has nothing to do w/ wireless.
Go to router's setup pages, you'll find one of them to do with Wireless, Wireless Security. In there you can review or renew your security passphrase -- you'll then have to apply the security type and passphrase to your wireless adapter.