Impossible to view complete content

Since a few days it is impossible to view the complete content of some incoming mail. Some parts of the page(s) are shown as white boxes with a red cross. I use explorer 6.0 and outlook 2002. Even the old messafes, received before the update, I can not see properly any more. So it is obvious that I have a local problem, but where and how?
I would be very grateful if someone could help me.