Unable to reinstall Battlefield: Bad Company 2

...or any other game for that matter. You just uninstalled your game for one reason or another and now it simply won't reinstall. This happened for me with Bad Company 2:

After inserting the key the installer simply won't pursue the install process and will close without warning. The solution was simple (that is, after I looked around for weeks), in fact you are simply missing some Windows Installer files or Windows Installer is defective.

1. Go to Microsoft's Download Center and search for Windows Installer.
2. Download the newest Windows Installer redistributable for your system (4.5 for XP and Vista).
3. Install.
4. Reboot.

That's it. You now can go back to play BC2.