Help! Why isn't my mp3 player showing up on my computer?

I figure it’s the USB cord that’s messed up, because a few days ago it was working. The mp3 is connected, but right now it is not showing up on “my computer”. I want to add songs so I don’t know what else to do. Other times it will be plugged in, but the player will be only charging, and not actually connected to the computer to add/delete songs.. What should I do ? I don’t have another USB at the moment and I’m trying to get this fixed. It’s a Sansa USB player. Help! Thank you :)