DESPERATE HELP! MacPro 2014 suddenly fried(?) after inserting external USB HD, help!!!

I plugged in a brand new USB external HD (literally out of the box) to my MacPro and suddenly the displays went dark, the music stopped. I waited a few minutes and tried to restart. The chime goes off but displays remain dark. I think I tried everything under the sun (PRAM reset, 5 second long hold of power button) but to no avail.

I've removed all cables, left it unplugged a minute, restarted without anything except monitor and keyboard. Chime happens then nothing.

Is it possible the USB drive fried the mobo?!? I've had this Mac for a while now and never witnessed something like this.

I have two external monitors attached via thunderbolt

This is the HD, an INATECK SSD optimized enclosure

http://www.amazon.co.uk/gp/aw/d/B00FCLG65U/ref=mp_s_a_1_1?qid=1455046541&sr=8-1& pi=SY200_QL40&keywords=inateck+enclosure&dpPl=1&dpID=41LT5jGJ01L&ref=plSrch&th=1 &psc=1

http://www.amazon.fr/dp/B00FCLG65U/ref=pe_386181_40444391_TE_item