My samsung YP-U4 mp3 player worked fine on friday, i plugged it onto the usb port and it charged. The next day, i plugged it onto the usb port and it doesn't charges, and the player doesn't recognize the mp3 at all. What happened?

Hi,
Download the latest driver software from the Samsung website with the link below and install it on your PC. Click on downloads > Software.
If that doesn't fix the problem, try connecting it to other USB ports as the one you tried could be faulty or some USB ports do not provide enough power for the device to get connected.

http://www.samsung.com/my/support/detail/supportPrdDetail.do?menu=SP00&prd_ia_cd=&prd_mdl_cd=YP-U4AB/XME&prd_mdl_name=YP-U4AB&srchword=YP-U4