Q: what can I do with my iPhone which is not recognised by the PC during an update of the iOS ?

Trying to update iPhone 4S from iOS 7 to iOS 8.  All PC software up to date, and 2 phones and 1 iPad already updated successfully.

Old software was extracted, but upon completion of updating to iOS 8, error message (6) and "this phone could not be updated"

After several attempts, was offered message to "update" or "restore".  Update obviously did not work, so tried restoring.

This also failed.  Now the phone is "dead" shows no name on the PC, and bears an iTunes icon with  a plug connection icon - suggesting

I should plug it in to a USB port, when it is already plugged in.  There is no acknowledgement between the PC and the connected iPhone!