Please keep in mind before you read on that I've kept in mind that you're probably not a web designer and it seems you may not have full control of your website. if that is the case, let the positive criticism by myself and others who respond be passed to your developer and try to get some of the suggestions changed/edited.
Well your home page validated, that was good news off the hop for me.
Graphically: I'd make the small arrow under the red links at the top a horizontal bar rather than the arrow - I was unnecessarily distracted by that for some reason. Your website color scheme is slightly out of order. You have at least more than 5 different colors/hues.
I love a good footer: your footer looks dead and dry. Only because the color of the text is almost the same as the background - it doesn't stand out and say WOW. I'd change the color of the text to white. There is no reason to not make that part of your site nice on the eyes for visitors. Contrary to popular belief, people do go to the footer all the time to find links to pages like contact, about, blog, Facebook, Twitter...
In your footer use the following code for the copyright:
...and remove the link to the site designer. That link does you no good and more harm than anything - for now.
©<?php echo date('Y', time()); ?> Cornel Diagonestic - All Rights Reserved.
The header is rather large. I'm not sure how effective that is towards any of your marketing/conversion goals.
Your testimonials button link didn't give me a good or positive user experience. I was expecting to see a list of testimonials but instead found your form to submit one. That can be rectified by simply adding "Add Testimonial" to the button.
From an SEO/user experience perspective I would suggest that you add links within the copy of your articles to other pages within your site if the keywords are there. If the keywords of one article aren't on the page of another, simply edit a few of the articles with some copy which will enable you to create the link with the right anchor text.
Anchor Text is the text that the user clicks on - that should be a keyword.
Have a great day!