Here's one way:
Place this code in the head section of your page and customise it for your needs. As written here, your links will be bold and blue. When you hover over them, they will be bold and red with a red underline. They will return to bold and blue when not being hovered over.
<code>
<style>
a:link {text-decoration: none; color: #0000FF; font-weight: bold}
a:visited {text-decoration: none; color: #0000FF; font-weight: bold}
a:hover {text-decoration: underline; color: #FF0000; font-weight: bold}
</style>
</code>
Do not include the "<code></code>" on your page.