Hello...

I am having problem with my router. I am unable to use my 5GHz bandwidth but 2.4GHz looks fine. 
The 5GHz was working just fine a day ago. But I don't know what happened! It just stopped working all on a sudden. 
I've tried restarting it, rebooting it, resetting it. But nothing brought any satisfactory result. 
I badly need some help. Please!