Css...continued

I recently posted a question...

I have put in Css in my page. I want the link to be underlined when the mouse goes over it. Now, it underlines but when you click on the link and then put the mouse over the link, it won't underline. What gives?

I forgot to put the html so here it is.
<style type="text/css">
<!--
a:hover { color : none; text-decoration : underline; }
a:active { color : #ffffff; text-decoration : none; }
a:link { color : black; text-decoration : none; }
a:visited { color : black; text-decoration : none; }
//-->
</style>