I recommend that you start by fixing the
markup errors and
CSS errors reported by the online tools. Decide whether you're using XHTML or HTML, and stick with that. Don't mix them together.
Don't link to content-free pages. If you want to leave the link text as a placeholder, then go ahead, but don't make it a link. ("SERVICES")
Use a template system of some sort to give all the pages a similar look and feel. It's disconcerting to follow a link to a page that is supposed to be the same site but which looks very different. ("ABOUT US")