Stuck in soft dfu mode
Use ReiBoot app to push the phone out of recovery mode cycle. I had the same problem and only one that app solved it. I tried going into DFU mode and  without DFU mode, using .ipsw files to restore old and new iOS version, and none worked. I installed ReiBoot and in 5 minutes I solved the problem. Just install the app for mac (I do not know if it works for windows) and plug the iPhone in the computer. Open the ReiBoot and push the phone out of recovery mode cycle. VOILA! This was the only thing that worked for me. Nothing else worked. I tried different USB ports, different USB cables, nothing else worked, literally.