If the phone is getting restarted then you will have to reload the OS of your phone.
You can download the phone OS from :
http://us.blackberry.com/support/apps-and-software
select your carrier and the desired OS for your phone as you wish. then download the application loaded which helps you to install the OS to the phone from your PC. We call it as BBSAK (BlackBerry Swiss Army Knife).
You can get the loader at :
bbsak.org/download.php
Once you are done downloading the both. Install the BBSAK and the Phone OS to the computer first where you downloaded from the blackerrry site.
Connect your phone to the PC via the Data cable and wait a few seconds. Now open the BBSAK software and click CONNECT. As soon as you do it your phone's IMEI number will be displayed there. So now click Wipe device and press o for any upcoming messages.
Now look at your phone, you will see a message saying that the phone is getting wiped (Resetting).
Wait a few minutes and once the wipe it done Click on LOAD OS on the BBSAK software and then you will get a menu to select the Blackberry OS that you have installed in the PC (Remember i said that you need the Blackberry OS to the PC first). So now select the OS and then click Next and the rest is just a few steps left with some more Next clicks.
I hope you are now done with the New OS installed to your phone. Keep posting if you need any further help.
Don't get scared, you can do it all alone. Try it ok ? 
Click LIKE on this if this helped you.
Cheers!
