Hi
If you have images (e.g. jpegs) showing OK in your media list (as thumbnails) and you are dragging and dropping them onto the video track and they are appearing there as thumbnails as well (or clicking them and adding them as per the prompt), then you aren't doing anything wrong.
If they aren't in the left preview window when you click them to select or they don't appear in the right hand pane when the sequence cursor is dragged onto them and they don't appear when the sequence is played......then there is something wrong.
I would suggest you reload the software again and see if that makes any difference. What version are you using?
Nat