If you have shell access, you can check whether the upgrade process is running. If you kicked the web based upgrade script, it is possible that a browser timeout stopped it. If that is the problem, then worth trying the CLI version of the upgrade script. But you have to restore the 4.0 backup before that.
No, I don't know whether the upgrade to 4.1 takes longer than usual - it was released just yesterday!
No, I don't know whether the upgrade to 4.1 takes longer than usual - it was released just yesterday!