After installing iOS 8 on an IPad Air Mini Retina and latest gen iPod, both worked fine until I performed a reboot (Home & Power buttons) on both. Now, neither will start up. The Apple logo appears on screen, eventually fades and then turns off. I have repeated the reboot process several times now but I am unable to get either device to start. Accordingly, I'm not going to upgrade my 5S or other Apple iOS devices. Any ideas what to do? HELP?