I recommend that you start by fixing the
markup errors and
CSS errors reported by the online tools.
Don't use px for font sizes on web pages. Use a font size of 100% for body text, larger percentages for headings and the like, and (slightly) smaller percentages for legalese and other fine print.
Four columns is a lot for most displays. Each column gets squeezed pretty badly.
It wasn't obvious at first what AD REM company does. A good
tagline could help. I was able to figure it out from the menu across the top of the page, but many readers will ignore banners and menus, and will look only at the content section of the page.