iPad 2stuck on progress bar after iOS 9

My folks gave me an old I pad 2 for my son. I updated to IOS 9 and it worked well. Then it kept going to the black screen with the apple logo and the progress bar. Its stuck about 1/4 done and cannot do anything. I have plugged it on to my iMac. It says you need to trust the PC to continue. But it just shows the loading screen. Any thing I can do?