I had this same problem last night. Just download you original OS for your phone and then use BB Desktop Manager to re install it. It will re-install your BB to the way you bought it.
Do a search for a link to your OS , your carrier website should have it. Download it to it's default location. It should be under c:/programfiles/common files/rim/shared. Then when you plug in your BB to your comp, run BB Desktop Manger and it should tell you to update, and then you pick your prefs from there. Hope this helps.