mjulian
Where is your actual library? Is it on an offboard storage device? If so, what you need to do is plug it into your new PC, and then you need to point iTunes to it. Click on:
edit > preferences > advanced
Then in the box that reads 'iTunes media folder location' navigate to your offboard device.
Then close iTunes, leaving (your offboard device plugged in), then open it again, and your library should appear.
If you have playlists and ratings, let me know - because to get those back is a different task.