Guest,
It's strange that you have to leave your player playing though.
It sounds to me that you might hve to check the OFF timer and SLEEP time as what I think is happening could be that your player switches off after a certain time and for some reason, doesn't then charge if it switches off.
Also, when you charge your player, do you use the [on/off] switch to turn it off? You shouldn't need to.
Also, while you left it charging on your computer, was your computer ON? You computer will need to be on to charge the player.
Here's some things to try:
1. Set a time/clock setting in your player.
2. Go into the settings of your player and chance the settings for 'dark', 'darkle', 'sleep' and 'off' time to ZERO instead. This should now disable your player from going to sleep or turning off the screen.
3. Now leave your player charging on your computer. Remember to leave your computer ON as well.