When attempting to boot from the 64bit ISO is starts loading the WinPE environment, so I can see the windows flag, but then after a few minutes a quick message pops up on screen that I've never been able to fully read, but the top line says something like server must restart and the server just reboots.
This particular server only has 4GB of RAM, its just an old test box we use for testing things like this.
This is not limited to this one old Dell server by the way.
I also tried this on a newish HP gen 8 blade server and the 64bit ISO crashed that too, but the 32bit ISO worked and that server has Server 2012 R2 on it.