Did you let the battery completely run out?
If so, there is a solution.
Don't use the computer, use your supplied charger. My mp4 came with one which has tho LEDs, one red that indicates proper conection to electricity network and another green which indicates mp4 charging.
However, I know some chargers that have only one LED, and it will change color from red to green. The colors have the same meaning, and the green color problem is the same.
So, here is what you have to do:
1. Plug the charger to any wall outlet, and make sure the red light will turn on (or the LED will turn red).
2. Turn on your mp4, It doesn't matter if it will not power on.
3. Plug the mp4 to the charger using the cable. Soon you will see the Conection screen and the charging animation. You will notice that the green light will turn on (or the led will tunr green on the second case). The problem is that as soon as the mp4 screen blacks out (for power saving) YOU WILL NOTICE THE GREEN LIGHT TURNS OFF or goes very opaque. DO NOT LET THIS HAPPEN, as this is the reason your mp4 will not charge!!! If the screen goes black and the green light fail, unplug evetything and start over again.
4. On Conection screen and BEFORE the screen goes black press M key to go to Main Menu (the green led will turn off, ignore it). Then, enter any function you wish. I found FM radio will do the best, but however you can try playing music. Do not use movies. Notice this time that when the screen goes black THE GREEN LED WILL TURN ON!!
. Don't let the screen turn on again...DON'T TOUCH ANYTHING OR YOU WILL HAVE TO STAR OVER AGAIN!!
5. Let the player gently rest, without pressing anyting, charging peacefully. Now walk outside, rent a movie, buy some pop corn and wait about two hours for your player to be ready. Watch every time to time that the green light is still turned on and shining strongly (without touching anything...remember that as long as the screen is black the player will charge).
6. After ablut twho hours the green light will turn itself off. This is good, it means your player did charge. Now unplug it and test it. Mine had the same problem and was rescued this way. From now on, you yill not need this special procedure to charce it anymnore.
7. Remember, DON'T let the battery dry out completely. This is why this problem happens. As soon as your battery status shows you the battery is empty, charge it.
Notice also that you will have perhaps to play a little for this to work. Try several times if you do not succed the first time. The problem state is green light turning OFF when screen goes black, you have to achieve your player to do the opposite: green led turning ON when screen goes black.
GOOD LUCK