The SDK Manager is located under the C:\Program Files\Android\android-sdk folder. It will list the components that have been installed for the SDK. If you don't see the platform-tools package is installed, then select its checkbox and install it. An easy way to tell if the package is installed is to verify that you have the following file folder: C:\Program Files\Android\android-sdk\platform-tools
Edit: Ah, helps to read the original message, sorry. If you're having problems launching the SDK Manager, then double-check that you have Java 6 installed. It could be that the SDK Manager requires the latest version of Java be present on your machine...