Hello Martin,
Briefly (since we don't officially support Hauptwerk v4 any longer):
The problem will be that your computer has changed the name that it is presenting for the Launchpad MIDI device, which will make it appear to be a different/new device to any MIDI software. Hauptwerk v6+ has a mechanism for migrating MIDI settings from one MIDI port/name to another, but earlier versions didn't, so in v4 you would indeed need to auto-detect your settings again, I'm afraid.
Since you still have your original drive (and assuming that you could install it and that your original settings still worked in it, i.e. that the Launchpad device name remained as it did originally), if you wanted to upgrade to v6 then you would be able to migrate the Launchpad settings for your new drive (i.e. to whatever name the computer then presents for the Launchpad). See this topic for that: viewtopic.php?f=4&t=19543&p=146758#p146691