Disappearing images on Outlook Express 6

This is my first message to this group so I hope I have the right one for
this sort of question.

I have an unfamiliar problem with Outlook Express 6 that I cannot solve.

Nearly all my emails from commercial sources to which I subscribe have
suddenly stopped showing any images - but I can see the text. But, very
occasionally after a minute or so the images will appear. Yet the images are
there all right because I can frequently copy and paste them into another
programme where they do show themselves - but not always. In addition, if
these images are hyperlinks then they work even though I cannot see the
image but just the curser turning into a hand when it hovers over the
invisible image.

So I have
1.. Sent images, JPG and GIF to myself and they work.
2.. Got friends to send me images and they work.
3.. I have checked TOOLS/OPTIONS/SECURITY to make sure that the BOX "Do
not allow attachments to be opened that could potentially be a virus" is
unchecked.
4.. I have turned off my Norton email protection.
Then I ran out of ideas. So can anyone suggest what the problem is please?

I use Win 2000. Yes I know it's out of date, but just haven't got round to
changing it.

Many thanks

Baz