Unless it was Cubase LE, which would give a new soft-elicense number on a different computer, that would require download of a new activation code from Steiny. That is as easy as entering mysteinberg, and requesting a new code. Well, if you actually registered to begin with. Otherwise, just having the LE disc, and registering a new account should work just fine.
If a full version of C4,5 or 6, and no dongle, well, there will be not much help from here, nor Steinberg.