I left my mp3 in the car and i chare it and the screen turns all white

Let my try to decipher..

You left your MP3 Player in the car charging?

I once left mine on my charger for too long. I too got the "white screen of death".. Just hold down your reset button 'til the thing turns off. Leave it alone for a while, then turn it on and try to run down the battery a bit. It's just overheating.

 
saying that the display can be overheated and allowed to cool.. and then the electricity sent to the liquid in the display might cause it to all come back in an organized fashion.
if it does happen, you will probably have stains and spots in the display.. seen as brighter and darker spots.
but
it is better than the display not working at all.

pretty fancy stuff to have it all go back to normal after being overheated.
and if it works once, that doesnt mean it would continue to work again and again.
if the manufacturers decide to give you a 'chance' to fix your display once, some people might think it is okay to let it overheat all the time.. and then those efforts get wasted.