What is the symbol with the red square, green circle, blue triangle preventing opening images in IE7?

[Sigo]

What are these symbols in little boxes in the upper left corner of where images should be for links to certain sites on the web, normally video links to YouTube for example. Why does this replace the pictures? I have checked security settings and re-loaded Flash software, but it makes no difference. What's irritating is that it used to be okay on Explorer and has only recently reverted to these symbols. It's ok on my wife's Apple iBook/Safari, on a friends' XP with IE7 and when I try with Firefox. I have Vista Ultimate.

[Ethel]

I don't know anything about Vista but check your browser options - are you blocking images?

If you turn your firewall off temporarily does that make a difference?

[Sigo]

Thanks Ethel, have tried both, sadly makes no difference