Please provide the detailed information about the above problem.
1. Which Operating System are you using on your machine.
2. What is the exact behavior when you try to launch Adobe Reader ? Does it throw any error ?
3. Which version of Adobe Reader is now installed on your machine?
At the mean time you can also do the following:
1. Remove the current Adobe Reader installation from "Control Panel -> Add or Remove Programs".
2. Reinstall Adobe Reader (Get the Installer from http://get.adobe.com/reader/enterprise/ ).