Shoutbox

Ok, TO uninstall Windows Live Messenger (WLM):

1. In the notification area of the taskbar, click the Messenger icon, and then click Exit. *Only if WLM is running*
2. On the taskbar, click Start, and then click Control Panel.
3. Under Programs, click Uninstall a program.
4. Double-click Windows Live Messenger.
5. Click Yes.

To install WLM:

1. Download from here.
2. Follow the on screen instructions and when it asks you which programs you wish to install only have the check box beside Windows Live Messenger checked.
3. If it asks to restart your computer do so.
4. Sign in.

If the problem is still happening, tell me and i will instruct you on the next thing you can try.

[EDIT] You could also try this

Hope that helps