‘http error’ When I upload images in a post

I am so frustrated with this problem. When I go to enter a post with an image. I upload the image from the same folder on my hard-drive and it says ‘crunching’ Then displays ‘http error’
The unfortunate thing is I am completely computer illiterate !!
However if you have any advice whatsoever, I would be so grateful. I can battle to understand myself or pass onto my web-designer.