I developed my Drupal 7 site in a sub-folder of one of my portfolio sites, tested a move to a sub-folder in another of my portfolio sites. Everything worked fine in all browsers. I then moved the site to a different hosting provider as a subdomain of its parent site. Here Internet Explorer won't load the stylesheets, even though the site works fine in all other browsers. I did set the "Aggregate and compress CSS files" feature and clear the cache, because I know Internet Explorer has issues with loading more than a certain number of stylesheets. The site is a sub-theme of Zen. The only stylesheet that I personally added was my style.css. Everything else came with the theme. I have searched everywhere for an answer without success. Does anyone have any suggestions?
View the actual source and see what path it's trying to load from. This should get you going in the right direction.
Have you tried with agregation turned off? The only thing that comes to mi mind is that there are issues with files permissions.
The IE CSS problem where IE doesn't load more than 31 stylesheets has been fixed in D7 (https://drupal.org/node/228818) so the chances are that's not the problem. I too would recommend turning aggregation off. And also, load the site in two separate browsers (say Chrome and IE or Firefox and IE), switch on developer tools in both browsers. Find an element that isn't styling properly in IE and look at the classes to see which ones aren't being loaded and see if you can narrow it down to a particular module and, if possible, post your results here.