Error -1 after IOS update

Hi,

i have a big problem with my Ipad Air 128GB Wifi+ Cellular.

I tried to update my ipad to version 9.3.1 yesterday. After the update the ipad had a black screen with the itunes logo in the middle with a usb icon. I paired it with itunes and this is what it said:

"The ipad could not be restored. An unknown error has occured (-1)."

I tried to restore it with different USB-cables on different laptops (windows 10, windows 7) with deactivated firewall and deactivated anti virus and current version of itunes.

I always get the same error...

Before the update the IPad worked perfectley without any error or problems. I updated it many times before, never had any problems... and no it seems dead.....

Please help.