Trouble transferring downloaded music files to new laptop

After my laptop died, I have manaeged to get all my old music files complete in their old folder onto a portable hard drive. The new laptop has now got itunes on it (good) and has access to everything which I have purchased via the cloud (also good) but won't recognise everything that I have ripped from CD (very bad as this is about 15,000 tracks).

How do I get itunes to 'see' and access all of my old files? I have used preferences - advanced - change media folder location to the new location - but to no avail.

I really do not want to load everything up again...