How come some of the blue text are not links whereas the other blue text are links? The same goes for gray text. Everyone needs to learn how to use a website before they can easily traverse it. By mixing things like this up you are providing an extra learning step to something that can otherwise be easily learnable (because it would be the same), i.e all blue text would be hyperlinked and grey non-hyperlinked. When provoking another learning step it's important to consider that some people have learning difficulties and small cognitive loads (they can't remember much).
Your search input field doesn't have a label & you're using an image for the submit button, so there's no way of knowing what it does & what information I have to enter if I'm using a screen reader. If you can't use a label then use an "alt" attribute on the submit button and give it a descriptive value.
Text is generally quite small and because of this you ought to make sure it has good readability. At the moment I think you can see how it can be interpreted as difficult to read. There are tools to help you make text more readable, such as the Colour Contrast Tool from Jonathan Snook.
Try not to put "height" CSS styles on things that contain text because that sets an absolute value that does not change size, even if the text within it resizes. For example, I resized the text (text alone) to 200% so that I could read the text easier and it was cut-off on the welcome section [screenshot]. You can usually achieve the same thing as "height" by using "min-height" instead. You don't have these problems with "min-height".
A lot of your images don't have proper "alt" values.
<img src="http://www.biginjapan.co/biginjapan/biginjapan/wp-content/uploads/secpluslogo.gif" alt="http://www.biginjapan.co/biginjapan/im-now-comptia-security-certified/">
They don't all necessarily need any value in the "alt" attribute if they have headings and/or text nearby that describes them (but all images need an alt attribute even if its empty).