no image – filename & red cross?

I was uploading images fine until about two weeks ago. I am now unable to get an image on the weblog. When I upload it takes its time as though it is actually going through the process, there is no error message; however, all I get is a white box with the filename and a red cross in the corner.

I am a newbie to the world of wordpress and no working knowledge of code or even where to find the folders where wordpress is installed!

Thanks in Advance