Windows 8 should not really make that much difference to that fact that iTunes needs to locate the music. i suspect (as others have mentioned) that you have simply told iTunes to play music from a CD and then simply taken the CD away.
If you don't have too much other music copied over, it may be easier to start again by uninstalling iTunes (this is not a delete of the shortcut), deleting the iTunes folder from your music area. Once you are clear of everything relating to music and iTunes, copy the contents of the iTunes music over to the
standard location then re-install iTunes. It will upgrade the iTunes database that it finds in location and add your music automatically because it has upgraded the database with the newer version. This is the easiest method, otherwise there are ways and means but on a new machine, it should be easier to do this. Let me know if you can't and I can talk you through it either over the phone or via PM... If you were nearer to me I would offer to assist in person, but I have a feeling you are not in Cheshire if I recall correctly.