From the screenshot, it looks like you are trying to create an admin account. Were you asked to enter your password when you tried to do that, or did you get the error directly (the error could be because of insufficient permissions).
Since the graphical appraoch doesn't seem to work, try it through the terminal. Open a terminal and type:
sudo adduser --gid 4 <username>
You will be prompted for the password for this user and some additional details that you can leave empty. You should be able to logout from your user and log back as the new user, which should have admin privileges.
Not sure if this will help with your overheating issue but if you don't experience anything once you are logged in as the new user, that might mean some startup application is running when you log as your original user. Although anything that managed to get itself installed like this will likely affect all users as well, but is worth a shot.
EDIT: While youare in the terminal, you can also try the following:
sudo cat /var/log/syslog | grep user | less
This may show something interesting about the errors you were seeing.