Well, if harddrive had been taken out of the PC, than it must have been shut down. Than it must have disappeared from the network. Possibly you should search for some kind of software which would ping all the PCs and alert you.

Of course you should change passwords. If the harddrive had the admin profile on it than this is the onle way. If the profile was loaded from network than it's ok.

elen sila lumenn omentielvo