Classic theme?! My eyes!
Looks like IE 8. I set my theme to classic and IE 8 looks exactly like that. Also it looks like the compatibility view button is "pressed" next to the address bar and lock icon.
What you have here is
Under these conditions it's going to be horribly slow and broken. Tell the client to stop using this browser, or at the very least, stop using compatibility mode. They may not have enabled it intentionally; it could be because they have other websites that need it and it's just defaulted to enabled everywhere.
P.S. - Yes, I still have IE 8 installed, but it's not by choice, as I don't own this computer. I use Chrome as my main browser, though. :}