New
#21
I had the exact same problem. This may seem simplistic but here's what worked for me before I even saw this thread.
I told each of my machines to leave the Homegroup, then turned all of my machines off. Then I turned on just one machine to create a new Homegroup and this time it worked. After giving that single machine several minutes to load up and settle, I got the prompt to "Create" a Homegroup instead of "Join". Once I created the new Homegroup I turned my other machines back on and was easily able to join it with the new password.
Apparently Windows 10 requires there to be no other machines running on the network in order to create a new Homegroup.