5 ghz just stopped working - help

I've been running my original 1 TB Time Capsule connected to my cable modem in n only 5ghz for months.

I have Airport Extreme connected in another room connected to a couple of HP printers so we can print wirelessly.

And lastly an original Airport Express connected to the Time Capsule via ethernet cable to have g available for our iPhones.

All has been working flawlessly for months.

Today I closed my MacBook Pro and went out. Hours later I came back and opened my computer and it didn't seen the Time Capsule n. It wasn't even showing up in my Airport Menu. I could see the Airport Express g fine. And could connect and surf the web fine. But the Time Capsule was nonexistent as far as my computer was concerned.

So I restarted everything. Nothing. So I did a soft reset of the TC. Nothing. So I did a hard reset and reconfigured. Nothing.

So out of the only left to do was to set the TC in n only mode at 2.4 ghz. And my MacBook Pro sees the TC fine in 2.4 ghz. But in 5 ghz the TC is invisible. Even though this has been working fine and fast for many months.

Any ideas? Why 5 ghz only would not work? Why 2.4 n only works?

I'm at a loss. Could the 5ghz band "break"? But 2.4 ghz be fine?

Thanks.