To bring up the manage widgets window you must have pressed the + sign. But this also shows a horizontal display of all installed widgets too.
Have you tried pressing the F12 key or pressing the button on your mouse, that is if you have the Mighty Mouse and it's configured to show the Widgets when you press the button. The same goes for the F12 key, you may or may not have re-configured that key to perform another function.
The OS pre-installed widgets live at:
MacintoshHD ~> Library ~> Widgets
Any subsequent 3rd party Widgets you've downloaded/installed would live here:
YourUserAccount ~> Library ~> Widgets
Let us know what you see at these locations.