My iphone 5 won't download all its music onto our new computer its windows 8 lenovo?

Ok so everytime i plug my phone into my new computer itunes comes up but it won't sync my stuff at all. All that comes up is go to itunes store or something else i forgot but when i click on the other thing nothing happens and i need my music and phone to sync to our new computer but it won't!

Simple way is this when you plug in your iPhone, It will show import pictures and videos or import music. Simply import it from there!

When you connect iPhone and sync with iTunes, you will transfer the music files from iTunes to iPhone, but can't transfer music from iPhone to iTunes. You may use some tool to transfer files from iphone to PC or itunes.here is a guide of iphone transfer.