Download the same OS as is on your phone to your PC. Double-click the exe that you downloaded. That will install the OS on your PC. Then go to C:\Program Files\Common Files\Research in Motion\AppLoader\Loader.exe, run Loader.exe, and let it reinstall the modules you need.
If you are running the latest official release from your carrier, you can normally get it from your carrier. If you are running an older official release, you will probably have to upgrade to the lastest official release. Carriers don't normally keep obsolete versions available. If some other carrier has released a later version than your carrier, and you are running that, you can get it from that carrier's site. If you don't know what OS version you are running, type myver and click the space bar twice. You'll see something like 8330/4.5.0.75. The number after the /, all four fields, is your version number.
