Re: BB 8520 won't turn on!!
First, if you have a microSD card installed, remove it and try again.
If the card is not the problem, try this and see if maybe the problem is just a dead battery. Plug the BlackBerry into a wall charger and leave it for an hour. Maybe the BlackBerry will boot when the charge is sufficient. If not, remove the battery for a moment while the BlackBerry is still plugged in, and re-install the battery. See if the BlackBerry boots.
If the BlackBerry still doesn't boot, you need to try another battery. Borrow one if you can, for a test. If you can't borrow one, then buy one, and buy a genuine BlackBerry battery.
Note: The above is conditional on the assumption that the BlackBerry is not broken. If you have dropped it hard prior to this problem, or gotten it wet, all bets are off.
Posted via BlackBerryForums.com Mobile