How do I fix my default mail to be yahoo?

I don't know what has happened but yahoo is no longer my default mail. I have gone to the internet options to reset it but it is not listed as a choice. Is there something like an update that I can download to fix this problem?How do I fix my default mail to be yahoo?
To setup yahoo email as your default mail using Internet Explorer.

Click this link for instructions.

http://help.yahoo.com/l/us/yahoo/mail/or…



To setup yahoo email as your default mail using Firefox 3 (Yahoo now recommend you use this browser).

* Download and install firefox 3 http://downloads.yahoo.com/?p=win

* After installation and when you have Firefox 3 up and running, click ';tools';, then ';options';.

* In the options window that pops up, click the applications tab.

* Scroll down to “mailto” and change to “use yahoo mail”

* Finally click “OK”.