Default [Q] HTC One Mini won't turn on - blown up already?

Oh dear - I bought a One Mini from eBay just before Christmas, was brand new (still sealed). Was really enjoying the phone until today when it just turned off in the middle of me browsing the net on it. It was on full charge!

I've spent ages trawling around online...tried all the hard and soft reset key combinations, none of these work. Have tried charging it - the LED lights don't come on, nor does the screen. I've tried plugging it into a laptop but it fails to install a driver, it just stays as 'QHSUSB_DLOAD' in device manager. Tried installing the HTCOneToolkit and using that driver button, but it seems to just launch the first pop-up then does nothing, tried doing an install driver and browse to the HTC directory but that doesn't find the driver. Tried different USB ports, resetting the laptop, tried HTC sync manager, tried standing on one leg and screaming, but no.

Madness, all I was doing was browsing an ebay shop on the Chrome app, how has that bricked it?!! Any ideas how to fix?

Have contacted the seller to see if they have a receipt failing that, going to try HTC direct. What a faff.