Cannot visit website via IE but can open database via notes, why?

I met a problem these several days, all users could not visit our website through IE at some time, what they see is a slow running progress bar on IE and then followed with a empty page, but the domino server is still alive and I can visit database files via notes client, how could this be? What could lead to this?

Sincerely thanks to all answers and suggestions

Eric mumu