||We had a similar issue a few days ago. Exporting the shapefile and displaying again did the trick for us, although we still don't know what caused the shapefile not to display at particular scales.
Also, make sure there are no blank spaces in the shapefile name, including the path. Although Windows supports long names and blanks one never knows whether all the other software products that you are using are fully backward compatible. Excel, for instance, will import the dbf table of a shapefile without complaining, but will truncate the name of a table saved or exported in dbf format to 8 characters.