How to transfer Music from my PC to my IPhone 4?

I have already plugged in my I phone into the computer and have opened up itunes on the computer. I know the next step is to select my device in the itunes menu, however, I can't find my iphone there. My iphone is firmly plugged into the computer and is on. I'm only enabled to download music onto my iphone that I have recently purchased, while I have trouble getting older music onto the phone? What can I do to help the situation?

Try turning on your iphone make sure you correctly plugged it in checked the computer to see it connected to the iphone

Well, you can use AnyMP4 iPhone Transfer software, which can transfer files like music, videos, pictures, etc.between iPhone device and PC. And it supports every versions of Apple devices like iPod and iPad.