Welcome to the community and thanks for posting.
I'm sorry to read you are having issues with the 5 GHz wireless connection.
If you log into the router does it show that the 5 GHz network is enabled? To do this type in 192.168.0.1 in the address bar, sign in with the details underneath the router and click into wireless.
Have you tried a factory reset of the router to see if that helps?
Let me know how you get on
New around here? To find out more about the Community check out our Getting Started guide