Look up the AllowBypassKey property in the help file. Apparently it's set to False for your database. You need to change it to True to allow the Shift key to work. This will apply to all users.
If you've already locked yourself out, you may or may not be able to get back in. It depends on whether you're using the standard File menu. If you are, open Access without specifying a database. Then choose the database you want to open from the File menu. The second time you do this, it will open to the database window.
If you've locked yourself out and you're not using the standard File menu, you'll have to open another database and write a routine to open the locked database as a second database (using OpenDatabase). Then, using the object variable representing the second database, change the AllowBypassKey property to True.
If you're looking for a way to create a "backdoor", try creating an AutoKeys macro. Select the key combination you want to use, and set the macro action to SelectObject, setting In Database Window to Yes. Or, you can use your backdoor to re-arm the F11 key by changing the AllowSpecialKeys property.
Another backdoor way would be to have your startup form check the value of the command line (use the Command() function) for a secret word. Then start your database with a custom shortcut containing "/cmd secretword" at the end of the Target field. If the form finds the secret word, it can show the database window or allow special keys as above. Rick Sprague