Dislay problem with IE8

Run each webpage you want browser-compatible through the W3C’s validator and strive for valid pages.

I already did and i found no errors

That’s strange, I checked the home page and found invalid markup.
https://validator.w3.org/check?uri=http%3A%2F%2Fwww.compsolution.nl%2Fwordpress%2Fzakelijk&charset=%28detect+automatically%29&doctype=Inline&group=0

I found the error! I made my own divs in header.php for displaying the header image with html text. I removed them from header.php and put the divs in my main page backend! than i removed the display:none codes in my style sheet! Thanks for the Help Andrew i will check the validation also again!