very simple. Right now your newsletter is hardly obvious. And you have a ,lot of excess white space on the site you could use.
So put up a sign up form on the right of your page. Make a bold offer like "Receive Monthly Tips on How to Keep Your Computer Bug-Free, Running Fast and Productive".
Read the advice here for more tips on designing the signup form. http://blog.mindvalleylabs.com/marketing/evolution-of-a-signup-form/
I have made the changes you suggested and were mentioned in the article. I have now added a picture above a sign up form on my homepage and are tracking the impact. I think the picture will make a big difference.
The second biggest issue I face is that people are not confirming their email. When someone signs up I point them to this instruction page to complete the double opt-in process:
http://www.pcshield.co.uk/Success.html
I think over the last 12 months I have "lost" a 1/3 of people because they don't confirm.