At the time of the reboot was your battery atleast halfway or was icon sitting at red?
•if it was red its unlikely to boot up because a boot up takes a lot out of it.
Steps to solve that are: Remove the battery and insert the charger and now reinsert the battery. Leave to charge for 3-5 hrs hours...if still no luck then repeat the whole procedure again.
•If the battery was full but now doesn't want to boot:
Try a safe boot by removing the battery and hold down back key and now reinsert battery when the loading is a quarter way release the key........if the phone boots up proceeding with deleting any installed apps then was installed just prior to this issue.
• If that fails then remove battery and hold down "end call button" now while holding down the button replace battery, when red led lights up release the button and press and the "call button " for 3 seconds and release and press "end call button" ...........continue this process and hopefully you see hourglass pop up. Once this occurs leave the buttons alone as it should boot up. Once it boots up leave on charge for 8 hrs.
Before seeking out repair centre try the following after first following all steps in 1st post:
1. open bb desktop software
2. remove the battery from your bb phone 3. connect the bb phone to the computer without the battery
4. the bb desktop software will give you the error msg bb desktop software cannot communicate with the connected device
5. click on update. the bb desktop software will check for available bb device software. note: if the bb phone has a password a prompt will appear to enter it at this point.
6. enter an email address or uncheck the option for email when new versions are available.
7. click install update
8. a popup will display that states that when complete the device will need to be activated with the wireless network. without disconnecting the device from the computer, put the battery back into the device and click ok. note: if you miss the opportunity to put the battery in the bb phone at the appropriate stage and the upgrade fails click "retry". if it continues to fail please start the process over again. note: once the upgrade is complete your bb phone will probably take 20 to 30 minutes to restart. this is normal behavior.
9. a msg will appear stating your software update is complete 10. click close.