My WordPress blog (world wide web.itauthor.com) shows all right in IE7, IE8, Chrome and Opera. However, it does not display whatsoever in IE9, even when I F12 and alter the display modes. Crippling all active WordPress plug ins does not solve the issue but switching to a different theme does - so there is something during my theme that IE9 does not like.

However, I like the theme I am using, I have used it for a long time and that i really don't wish to need to switch styles (and become confronted with hrs &lifier hrs of PHP fine-tuning) just due to IE9.

So what's the easiest way of searching for what's leading to IE9 to blank my website?

Try passing your website via a validator to determine potential issues.

http://validator.w3.org/

You will find a number of issues, it might be better to make certain that the markup matches your doctype. It's also wise to remove any whitened spaces prior to the doctype declaration (you will find 3 blank lines)

As the doctype is XHTML, you need to close your tags correctly. The 3 css link tags on the top isn't closed, change these to:

    <link rel="stylesheet" href="http://world wide web.itauthor.com/wordpress-content/styles/blueprint/screen.css" type="text/css" media="screen, projection" />

    <link rel="stylesheet" href="http://world wide web.itauthor.com/wordpress-content/styles/blueprint/blueprint-wordpress.css" type="text/css" media="screen, projection" />

    <link rel="stylesheet" href="http://world wide web.itauthor.com/wordpress-content/styles/blueprint/print.css" type="text/css" media="print" />

You are also closing some paragraph tags where they are not open. Just come with the issues around the validator page.

Despite everything, I've got a fresh installing of IE9 with default configurations, as well as your page renders all right. For those who have any IE add-ons installed, make certain you take IE9 without addons while using shortcut within the start menu and test again.

You might try:

<meta http-equiv="X-UA-Compatible" content="IE=8" />

like a workaround until the issue is solved.