MY MP4 PLAYER WON'T WORK IT TURNS ON A BLACK BLANK SCREEN LIGHT. WHAT SHOULD I DO ?

Check power settings and scrennsaver time.

Depending on how expensive the MP4 player is, you need to decide whether to replace the screen or buy a new one. Those are basically your only two options.

You can buy a replacement screen for relatively cheap, but it can sometimes be troublesome to open an MP4 player up and replace the screen completely. I would not recommend trying to do this, unless you have some experience with physically handling electronics.

I would recommend simply buying a new MP4 player. Maybe it's about time for you to get an upgrade anyways? Look of it as an opportunity to get a better one rather than the loss of the old one.

If you can add codecs, do so.

Creative knowledge base gives this answer for blank screen on a Zen MX:
White screens or blank screens could be easily resolved with a firmware reload. The following steps will take you through the troubleshooting steps.

1. Reset your player and verify if the screen is able to display its contents
   
2. Make sure that the player has fully charged battery
   
3. Finally, perform the recovery tool if the screen still does not display any contents properly through the following site:
   
   http://www.creative.com/products/mp3/MP3PlayerRecoveryTool/welcome.asp?

sir, the device doesnt work depending upon the place we are in.there must be some problem in its working.you better contact the company for replacing it.

it may be in lock mode and that can be caused by the battery running dry

you can see how to fix your problem at
http://www.mympxplayer.com/

I found the reset hole, it's okay. XD

it dont turn on

wen i turn on my mp4 (COBY) it only shows a white screen but i cant lissen to music or nuttin b.c it doesnt show the list.....wen i turn it on iyt juss has a white blank screen how can i fix this.....THANK YOU VERY MUCH