How many walls are between you and the router? 5GHz as I said, is harder to keep a constant connection to because it's not able to penetrate obstacles like 2.4 and lower frequencies can.
Your Internet crashed as in the service provider side or did your router crash? You might consider resetting it if you haven't already. Is the router rented from your ISP? If so you may call them to remote in and assist you in configuration, to take the heat off of you.
Is connecting to 5Ghz really that critical for you at this point or is it just something you really want to do?
I'm not sure what EXT is supposed to be, guest network maybe?
You really shouldn't notice any difference between 2.4 and 5ghz for gaming, I never have and honestly being 30-40 feet away might present issues where 5GHz is less useful than 2.4Ghz for a consistent connection depending on how your floor is setup and designed, what else may be interfering, etc.
Gaming on wireless presents its own issues, but don't expect 5Ghz to solve them for you, at least in any great measure. I've gamed on b, g, n, and ac. Honestly can't say I noticed a bit of difference latency-wise from any of them, but throughput is a different story obviously, and that's what 5Ghz is really aimed at overall. It's shorter wavelength should reduce latency sure...but if you want truly reduced latency, buy a length of Cat5E (terminated if you don't know how or have the tools) and run it to your location.
Do you know how to get into your router and check settings?
You can see the 5Ghz network, and cannot login? Does that mean you don't have access credentials anymore?
What exactly do you mean by your "Internet crashing". Did your service go out, was it ISP? Power outage? Router failure? Modem issue? Did you call your ISP for assistance?