iTunes won't sync music to iPhone 4

I bought a new laptop a few months ago, and installed iTunes. I moved all my music from my old laptop on to my new one, yet my iPhone 4 will not sync to it. I am not able to simply drag tracks across from my library and onto my iPhone, but instead have to create a playlist and autofill them, which means I can't delete or edit song information once i have put them on. This also meant i lost all my music when updating to iOS 5, and whilst I have got some of it back, I still have to autofill songs. If anyone knows how I can get back to being able to sync music like i could on my old laptop, please tell me, even if it involves resetting my phone/iTunes.