Songs wont copy to iTunes

There could be one or more of several reasons why you're having this issue.

To ensure a clean transfer of your library to a new computer you should have copied the complete contents of the Music folder on your old machine and pasted it in to the Music folder on the new machine. That way, iTunes would have used the control file (the .itl file) in your new library to find everything.

However, if some of your music files were stored in another folder, perhaps they have been missed in the transfer. For example, if you had files in the Documents folder instead, but only copied the Music folder, that would cause a loss of songs.

1. start by identifying what type of music is missing. Is it all purchases from a specific store, such as Amazon for example?
2. are the missing songs listed in your new iTunes library, but have an exclamation mark to the left of the song's title when you try to play them?
3. if you can see the file on your new computer, and double-clicking on it causes it to be played in Windows Media Player rather than iTunes, that will be because the default audio player is set to WMP, not iTunes. You can change that in Windows' settings; Settings/Apps/Defaults/Music player.
4. the step above (3.) will not cause existing files to be added to your iTunes library though. To add files that are not currently in iTunes, but are on your computer, use iTunes' top bar menu option File/Add File to Library and navigate to and select the file, or File/Add Folder to Library, and navigate to and select the folder as appropriate