You wont be able to access a local resource from your aspx page (web server). Have you tried a relative path from your aspx page to your css file like so…
<link rel="stylesheet" media="all" href="https://stackoverflow.com/CSS/Style.css" type="text/css" />
The above assumes that you have a folder called CSS
in the root of your website like this:
http://www.website.com/CSS/Style.css