Please provide the following information: Your OS and do you use iTunes as your media player? If so I have the solution. Did you try a search for your folders and/or songs on your hard drive? I bet I can help if you give a little more detail. I seriously doubt anyone "hacked" your system and got rid of just your music. Believe me--people that malicious wouldn't bother with just your music. Many of us can help but you need to provide more info. PM me if you want.
Best Of Luck