Can't create user

My computer shut down for no apparent reason. When I switched it on again, it didn't recognise my password. Luckily, I had another user and could log into that. The main user folder is in the home directory too with everything intact. The user has disappeared altogether from the Accounts pane in System Prefs. I logged in as root administrator to create a user with the same name as the folder. It all went smoothly and asked if I want to use the existing folder with that name as the home folder. I clicked OK but then nothing. No new user was created. I tried it several times. I even tried with a different name. It created a folder but no user. Can anyone shed some light?