There are quite a few possibilities here - none of them drastic or difficult to 'fix'.
Does this happen with every picture that you have downloaded, or just a few?
Do you have any other graphics programs loaded - if so, can you view the pictures using those programs?
If you open your browser (probably Internet Explorer), and choose File > Open, point it to look in My Documents and choose OK, are the pictures correctly displayed there?
If you right-click on one of the pictures that will not display, then choose Properties, what is the size of the picture?
If you have the picture and fax viewer program open, have you tried clicking the small magnifying glass icon near the bottom of the screen a few times, in case you need to zoom in?