I have the same... dvr - DS-7208HUHI-K2 , after firmware upgrade no user to choose, so can't login. SADP don't see it, but there is answer to ping via pc... I am tryging fix it second week in free time...
I can connect via putty, but there is no response to keyboard , can't stop booting via ctr+U, and can't put any command after dvr is up. I was looking for putty settings, because I am not only one with this problem ( no keybord response in putty) but I hope that somebody will help here
It looks similary to Gregs53 problem. thx