I had the exact same problem after recently upgrading to DNN 7.04.02. All modules showed expired. As someone else pointed out above, I went to the home page, clicked Page Settings, then just clicked Update and all is working again. However, this is the second time this has happened in a week. When this happens it also forgets which skin is being used for the home page - the setting in Page Settings is reset to default for the site.

This problem reared its ugly head again today. Previously as you had suggested, I went in and re-saved Site Settings as well as Host Settings. I see no reason why the platform would think all modules are expired. And what in the world does re-saving the home page settings have to do with anything? The entire site shows all modules expired, until I re-save the home page settings and all the sudden all the other pages come alive again at once.

Did you ever figure out what was causing this problem? I have a client that is experiencing the same issue on DNN Platform 7.4.1. They are on multi instance azure environments though and recycling the app pool seems to clear up this issue, but that is slowing down the site because we lose all of the cached information as well. Still trying to track down what is causing it though.