Try removing your caching plug-in if you have one.
I installed a plugin called Quick Cache ( A WP Super Cache Alternative ), and it worked fine when accessing WordPress via Chrome (which is what I normally use).
However, I noticed traffic drop off dramatically and finally realized that the Firefox and IE rendered a blank page when visiting the site.
I disabled Quick Cache ( A WP Super Cache Alternative ) and now everything is fine again. There’s no telling how much money that stinkin’ plugin cost me.