My coby mp3 player will not turn on

I know exactly what u mean. same thing happened to me.
Go into the coby media manager.
Click on music
when you list of songs appears, right click on a song
then click on syncronise.
do that for each song. this syncronises your songs to your player.
it worked for me!!!!
earlene

hold the play button pressed for a while. before that look if your player has a tiny switch(ON/OFF) on a side .

to turn this it off, hold down the Play/pause button

hold down the play button

Hold in the play button until red light comes on, once you have the MP3's on the device, press the play again to start the audio

hold the play button until the light comes on

The only thing I can think of is try new batteries. I know when mine plays and then shuts off by itself, the battery needs to be changed.
Hope it helps

Sometimes I must hold the play button down for over 7 seconds on my unit to get it to turn on. See also the answer to the question on properly charging the unit; i.e, have the slide switch in the "off" position.
If you are using a USB hub to charge the mp3 player then the hub must be powered.

Hold the play button down for 5 long seconds then release and wait , red light should come on. th en hit play again to play.

Check on the side of the player and make sure it is not locked that was why ours would not turn on. Once I unlocked it worked fine