If it is the MBL which is the problem, then specifically it will be the SMB (samba) server. That is the program on the MBL which serves the data to Windows machines. Just like there is a http (apache) server that serves up the webpage from the MBL.
You can test to see if the SMB server is actually running. You can login to the MBL via Putty via SSH. Then you can look at this link to learn how to restart SMB
http://community.wd.com/t5/My-Book-Live/Possible-problem-with-SAMBA-service/td-p/378981
In the event that you get an error message when restarting SMB or that it does not restart, then you need to reinstall teh firmware. You probably will not be able to do that from teh Dashboard, so you will need to do it via SSH by tricking the MBL into thinking it has old firmware and then updating it from firmware you have downloaded… http://community.wd.com/t5/My-Book-Live/Firmware-Update-via-SSH/td-p/310064
