How is a write-protection removed from music,pictures,etc from a computer?

How is a write-protection removed from music,pictures,etc from a computer? ?

I want to put some pictures on my Sandisk micro to show up on my phone and transfer some music to it also. But when I try to copy onto the micro, an error box comes up saying that it is write protected. I didn't protect the pictures or the music when placing them on my hard drive so why are they protected now? How do I change this? Thanks