NadineCat,
A few things to try:
Is it possible you have the views at a scale that is hard to see? Zoom out and ensure the drawings are not large/ click on the view bounding boxes and ensure the scale isn't small. Can you see the dotted view ports around where the views would have been? In the browser is there a lightning bolt next to the view - can you refresh the view?
Inventor will open a file even if the file associated is lost / broken. It is possible your assembly file/part files are not in the project location, so it cannot find them. They would have appeared when you first placed them, but then be lost later. In the browser, at the top switch from Model to Vault, and see if any of the parts have red arrows circling or ! symbols. They may need to be relocated or refreshed.
In the browser; are the parts/assemblies bold or greyed out? Is it possible the visibilty is off? Go to the view port, right click and select Edit. Check the View Representation and try switching to default or master.
Are the parts crossed out / lined out in the browser? It is possible they are suppressed. Go to the top of the browser and choose Level of Detail, Master.
Close the drawing, and in a blank screen (no part, assembly or idw) choose in the ribbon "Project". Under the option for Files, click add, and browse to the part / assemblie files. Select that folder. Hit save. Try opening the idw again.
I hope this helps. If any of the above did help, please select "Save as Solution". Kudos are nice, too.
-Kenny