does it power up? Is it frozen?
Try to remove the sim and re-insert it, I don't think that will do much though. The message "sim not provisioned" means the phone can see the sim and communicate with it but the sim is giving an error message in return. That same (not provisioned) message you get is the same if you tried an old sim that has been turned off by the carrier.
Im guessing your service is still active and in good standing? If so, I would go to the store and get them to issue you a new sim because the current one could be acting up. Also you can try to reset your network settings (in the settings menu -> General -> Reset -> "Reset Network Settings". Device will then reboot. You may need to enter your APN & MMS settings again, Im not sure.
Few people understand the psychology of dealing with a highway traffic cop. A normal speeder will panic and immediately pull over to the side. This is wrong. It arouses contempt in the cop heart. Make the bastard chase you. He will follow.