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And what is the problem?
Does the old HD contain a directory named 'Cdilla' on the root?
The directory will be hidden, so you'd have to show files with the H attribute before you can see it. Alternatively you can open a dos box ('Command prompt'), move to the root directory of that drive and type:
dir/ad
this lists all hidden directories.
If a directory Cdilla exists, chances are that you had a single user licence, protected by Cdilla.
There's no way to make that work anymore. PTC took the server off line by which you could repair licenses.
Additionally Cdilla doesn't function on 64-bit machines. It's a very dirty 32-bit trick, 64-bit systems don't allow it (with one exception: WinXP-64).
If a directory Cdilla cannot be found in the root(s) of (any logical partition of) that HD, then your license was most probably managed by FlexLM, either locally or via a remote server...
In the last case, no license file need be on that HD.
I suspect that with a 'no open and no asking for license file', yours is a Cdilla protected Mathcad 13.
Success!
Luc