Music sounds really bad

I recently moved my music library to a new computer and installed iTunes, thing is, the music sounds really good on the old computer and when I play it on the new one it sounds like I taped cheap speakers to my ears. The sound quality is awful and I don't know what to do, I tried the equalizer and still sounds bad, I changed every single headphones sets I have and still sounds the same. To describe the sound better, with my headphones it sounds empty, no bass and super loud S sounds. I don't know what to do as I've tried a lot of stuff to listen to my music on iTunes but I end up with a headache after 30 seconds of a song