How to Perform a clean removal of Windows Live Mail
The "clean removal” procedure completely removes Windows Live Mail from the computer.  Unlike the usual re-installation, this process requires deleting certain entries from your registry.  These methods may fix some installation issues and other problems.  Please follow the instructions below. 

A. Backup up your messages using the Export options.
Please refer to the steps in the following link:
How to backup Messages and contacts in Windows Live Mail

B. Removing Windows Live Mail
Please refer to the steps in the following link:
How to remove Windows Live Mail

C. Deleting registry keys
To delete the registry keys that are associated with Windows Live Mail, please follow the steps below.  Before you edit the registry, please make sure to back it up.  It is highly recommended that you know how to restore the registry just in case a problem occurs. For information about how to back up, restore, and modify the registry, please read the article in the Microsoft Knowledge Base at http://support.microsoft.com/kb/256986 .

Important Note: As long as the following instructions are done accurately, this should not adversely affect your computer and installed programs. 

For Windows XP

1. Click "Start,” click "Run,” type "regedit," and then press ENTER to open a Registry Editor window.

2. Click "HKEY_CURRENT_USER,” click "SOFTWARE,” and then click "MICROSOFT.”  Click "Windows Live Mail” and then press “Delete” to remove the registry key.

3. Click "HKEY_LOCAL_MACHINE,” click "SOFTWARE,” and click "MICROSOFT.”  Click "Windows Live Mail” and then press “Delete” to delete the registry key.

4. Exit Registry Editor and then restart the computer.

For Windows Vista
1. Open Registry Editor (Click "Start,” on the Start Search box,” type "regedit," and then press ENTER to open a Registry Editor window)

2. Click "HKEY_CURRENT_USER,” click "SOFTWARE,” and then click "MICROSOFT.”  Click "Windows Live Mail” and then press “Delete” to remove the registry key.

3. Click "HKEY_LOCAL_MACHINE,” click "SOFTWARE,” and click "MICROSOFT.”  Click "Windows Live Mail” and then press “Delete” to delete the registry key.

4. Exit Registry Editor and then restart the computer.