Tried to update my ipad air 2 through a computer, now my ipad doesnt work

While trying to complete a recommended update on my ipad air2 (which was working perfectly) on a computer I was able to get through "extraction" step ok but when given message that ipad was being updated in the second step it would stall each time and I received messages: unable to update, device not found, etc. I tried apple chat help, it wasnt helpful. Changed USB cable twice and computers twice. Help!!! All my important files are on this ipad and I cant get it to come on even with a "hard start up".

Any advice? Thank you in advance