Q: Apple TV "software for this apple TV is not currently available"

That is the Apple tv3. You should be able to download the software via iTunes. If not then you may need to take it into a store. Here are more detailed instructions....

Restore your Apple TV using iTunes - Apple Support

I got this message, but it went away if I had the usb cable plugged in BEFORE I connected the power.

I can't promise anything but it worked for me.

Thanks this "small" detail saved my day !!!

GDIT, it worked for me too, first the usb then the power

I also found that I got this error message when plugging my USB cable into my keyboard (which has a built-in USB hub).  If instead I plugged the USB cable directly into the computer, the problem went away.

EXCELLENT! You just made my Day. THX

After plugging out the power cable from the Apple TV and just leaving the USB cable it worked, I supposed one doesn't need to have the power cable connected during this process.

THANK YOU !!!!!!!!!!

Just to say that taking this advice, unplugging the power and leaving just the USB in, is exactly what fixed the issue.

Thanks!

I have no idea how or why you would even want to try that but it sure did work Thanks!

It works because there's power on the USB cable, so ATV boots up and senses the connection. If it's already awake when the connection is made, it doesn't detect it, because it only checks on booting. Sort of like those things you can only do on Windows computers if you do them before startup is completed.

worked for me ,thank you.