Often it is a matter of a user-defined CSS file or having Windows settings override those of the website, while others it could be as simple as having the zoom setting up too high or using restrictive security software. In short, there is no 'do this' answer...you have to go through a long list for each computer, a list that changes based on operating system and version of Internet Explorer.
Every now and then I come across a computer where Internet Explorer displays very badly. The fonts are huge, sometimes word overlap each other, images don't display, etc. When I check the IE config, they all look normal. Everything else on the computer seems to look and work normally but IE is messed up. Does anyone have any idea of what causes this and how to fix it?