My iPhone 6S is totally dead. Help please!

Hi, my iPhone 6S+ has been fine but is now totally dead. It was almost fully charged and i started using it. It crashed after 10 minutes and i restarted it. It kept rebooting up to the Apple logo, then crashed again, then rebooted and so on. I tried hard reboot (on/off button and middle button) with no luck.

Plugged it into my PC and opened iTunes, then rebooted. It can up with the 'repair fault' box and I ticked okay. It looked like it was doing something but after a while it just want back to the normal iTunes screen.

Now the phone won't do anything - totally dead. It's currently plugged in charging, but it should still be about 60 % charged. Any ideas? I've tried iTunes on my laptop - the laptop (and now my PC) say it's a faulty device and doesn't recognises it.

Thanks!