This is commonly caused by having multiple windows and/or reports open within QuickBooks which must be loaded each time you open your file. To speed up the time it takes to open your file, you can change your settings in your preferences to not save your Desktop View when exiting. Doing so will close all the open windows/reports you have open when exiting QuickBooks.
Closing all your windows/reports close on exit helps QuickBooks open quickly and prevents reports from becoming corrupt.
To change the setting in your preferences select Edit>Preferences>Desktop View. Select Don't save the desktop and click Okay.