To install / reinstall BlackBerry Messenger, you will need the device OS installed on your PC. The simplest way to accomplish both objectives is to perform the Memory Optimization Procedure that's linked in my sig. Forums Moderator Reed McLay created it to help people free up memory. Reed's procedure walks you through the steps to download and install your device's OS on your PC. Once you've done that, he shows you how to run the App Loader to install and remove applications. That's how you install BB Messenger.