Try a battery pull first, i.e. pull the battery out while the unit is on.
Was it dropped or something? If the battery pull fails, then you'll have to connect it to a pc, and then reinstall the software - I hope you've done a backup lately...
I just got it replaced. i didn't drop it or anything it was just in my pocket i pulled it out and it was flashing at me. When i got it replaced the guy tried everything to fix it and he couldn't.
The device was replaced, and it's working correctly, right?
If not, take the battery out, and the sim. Let it sit for a minute, then put the sim back, and the battery back. If it has a memory card, take it out, and leave it out - for the moment...
Once the battery is back in, it will power on. It should take from 2-4 minutes to get to the 'desktop' of the BlackBerry. If that fails, then I suggest installing the Operating System (O.S. that came on the CD you got in the box) onto your pc, run desktop manager, and then connect the Blackberry. From here, run the application loader - remember to choose the backup option (unless you have no data that you want to save)...
