Suddenly IIS gives out blank pages for all the domains in the server. Sometimes, the .html pages does not works which requires IIS reset . But in case of blank pages restarting the server becomes the option. Why these happens with IIS and any specific reasons for that to happen such as hitting memory, etc .
First you should check the source code of the returned pages to make sure they are empty. Try to see the response headers and the return code. If the pages are empty this means that the application is crashing before sending the response. Check the server logs (access and error) and the Event Viewer logs (application then, may be system).