To delete the USD cache, first browse out to your appdata folder in Windows Explorer. You can access appdata by typing %appdata% in the Windows Explorer navigation bar, which will take you to the user’s AppData\Roaming folder.
Next, delete the following folders, which will be recreated when USD loads:
You may also need to delete your IE cache. To do this, from Windows Start go to Internet Options, or from IE, go to Tools->Internet options. Select Delete:
And then Delete: