Database is not accessible after 'taking it offline' process failed
You should never do this using detach. Until we know more about exactly what state your database is in now, for next time, you should do the following:


ALTER DATABASE SET OFFLINE
For each file, ALTER DATABASE MODIFY FILE
copy the files to the new location
ALTER DATABASE SET ONLINE 
when everything is working, delete the original files


The reason you don't want to do this with detach, and the reason you want to copy the files instead of moving them, is because when something goes wrong in either of those processes, you have exactly 0 copies of your database. Or the situation you're in now.