An obvious problem is that you have to enclose attribute values between quotes:
<div class="nav">
<a href=".about">about DOEC</a>
</div>
<div class="about">
Then, do you really have a file named ".about" at the same level as the current page in your site hierarchy? You should stick to proper naming of files, and avoid using names which begin with a dot, because for several systems this indicates a hidden file (.htaccess on linux, for example). Why not simply naming the file "about.htm" and use
<a href="about.htm">about DOEC</a>
instead?