Have you been on this screen in your router's setup area and scrolled down and found Wireless Network (5.0GHz a/n) and enabled SSID broadcast?
If so have you been on this screen to see if it is enabled
If it hasn't been enabled do so and then see if the light comes on and that it can be detected by an appropriately equipped PC, i.e. it has 5GHz WiFi capability.
If you still can't get the 5GHz WiFi to work, try either reinstalling or updating the firmware. If there has been some corruption with the software reinstalling it may solve the problem. Here is a link that shows how to do it and also you can download it from there as well.
With regards to your 2.4GHz internet connection.
Have you tried accessing the router using WiFi?
Disconnect the LAN cable from the pc and connect to the router using WiFi. Once connected, open a browser window and type http://routerlogin.net in the address bar and see if it connects to the router's login page. If so it proves that you have a valid WiFi connection between the PC and the router. Entering the router's username and password on this page and gaining access further proves that you are connected correctly.
What actually happens when you try to connect to the internet using wireless? What error message(s) if any do you get?