Connection timeout

I'm trying to fix my wireless internet, I keep getting the "connection timeout" message on my macbook pro. I have tried:

Turning the airport on and off
Restarting my computer
Restarting the router
Forgetting the network and re-signing in
Using the network diagnostics
Clearing the PRAM
Deleting files from the system configuration folder under preferences
Renewing the DHCP lease
Changing the MTU size
Checked for and installed all updates

None of it has worked. The wireless works fine on 5 other devices I have tested, I have even forgot the network on the other devices just to make sure the password is 100% correct and it is, so the problem is definitely my computer, I can see the network with the wifi, and if I type in a wrong password it will tell me it's wrong, but if I use the right password I just get the "connection timeout" message, if I plug in the ethernet cable I have internet. So everything else works. I even tried connecting to a different wifi, and I got the same "connection timeout" message, and went through all of the above checks with that wifi network too.

The 3 yr warranty for my computer expired about two weeks ago, so if any one has any additional ideas of things I can try I'd like to know.