I just purchased a sansa clip. I was able to download some songs on it and then I let it charge. I then went to add more songs after I had unplugged it. I plugged it back in to my pc and it would not even power up. I even tried it on my laptop and it doesnt even get picked up as adevice. It will not power up or anything. Has anyone ever heard of this happening? Is there a way to fix this or should I just return it to the store?