Brooke,
Are you attempting to view your model from a viewport on a sheet layer while you are in the middle of model design? If so...I believe you may be missing the workflow direction of VW. Building the model on its respective design layers then selecting a front, side, rear view or iso view using the Number Pad keyboard with stack layers on will bring up the model in real time so you can see your desing and layout progress.
Viewports are the documentation devices used to present the model for publishing to a sheet. The fact that you can go into a viewport and and text, dimensions and graphic objects as an overlay on top of the view makes the presentational part a little easier but it should not be used to preview the model during design.
Just my thoughts...
Pete A