iPhone 6-iPad Air common problem

Dear guys;
I have an iPhone 6 and iPad Air with common problem.Customer say’s they suddenly turned off.I check hardware of them both.They’re intact and no physical or water damage is seen.I connect them to usb to try restore,they’re detected in DFU mode.Select compatible IPSW and it says "waiting for iphone" and "waiting for ipad" but nothing more happens.

PS: I have latest itunes,IPSW,and other devices have been resotred with the same PC.