go to your router's page 192.168.1.1
enter the username and password
Look under security under wireless settings and see if you're using encryption. If you are, you should just be using a standard encryption, nothing fancy.
Then, go to your ps3 and look at network settings. Make sure it's on the right network first of all, and then enter the password for your internet accessibility shown on your router page on the encryption portion.
Then have the ps3 test the connection.
If there is still a problem, update your router firmware by going to the homepage of the manufacturer and download the newest firmware. Everything should be fine after that.