Perhaps you already have done this, but if you text boot (remove the "rhgb" option from the grub menu) with each kernel, can you tell what process is going on when the new one hangs. And what process comes just after this process (with the old one). That would narrow the problem down to two processes. Also you can see any "failed" conditions on the way.
"Never let the task you are trying to accomplish distract you from the study of computers."