How to delete the list of songs on iTunes
Methode A:


Open iTunes
Go to Music
Go to the "songs" area where each song is listed on one row.
Select a song, then click Control - A (which will select all the songs in your library)  
Go to 'Edit' menu
Select 'Delete'


Methode B:


Close iTunes
Find the iTunes folder (C:\Users\username\My Music\iTunes)
Go to the Music folder
Delete all of it's content
Start iTunes again, all music should be gone


I'm not using windows so I can't double check