I've no idea what you've done, but your style sheet indicates an unordered list to create your menu (a common method), but your page code shows a table - hence other than some minor local styling, nothing matches up.

I recreated your code and substituted an unordered list in place of a table and although it's not what you describe, is beginning to work.

I got a yellow background with a (darkish?) blue/grey background for the tab, that changes to a lighter grey on hover.

However, the tabs span 100% of the page, so that's clearly not the only issue with your code. But if you add:

position: relative;

float: left;

to your

div.menu ul li a

css, and get rid of the table and substitute an unordered list, it all begins to work.