Cannot access internet

I have a dell latitude I am trying to use for my daughter. I am unable to access the internet via wireless. I can connect when using an ethernet cable. I have tried everything I can think of and nothing works! It is able to see that wireless devices are available and the wireless light is on. It tries to connect, asks for a password; then says it is unable to connect. I go through the diagnostics but nothing is resolved.
Thus far I have

uninstall/reinstalled drivers
gave it a dedicated ip address on the wireless router
Tried using a usb wireless device - didn't work

Thanks for all the help you can give, it is most appreciated!