When you click the Windows Explorer or File Explorer shortcut Pinned to the Taskbar, or when running explorer.exe directly in Windows 7 or 8, the following error message may be displayed with text "explorer.exe" in the title bar.
This file does not have a program associated with it for performing this action. Please install a program or, if one is already installed, create an association in the Default Programs control panel.
And using the WinKey + E key sequence causes "Unspecified error"
However, Windows Explorer may launch correctly when including additional switches such as /e or /n with explorer.exe, or double-click the (My) Computer or This PC icon. This problem occurs due to missing data in the "HKCR\Folders" registry key.
To fix the problem download Folder association fix for Windows 7 (via) unzip and run the REG file. If you’re using Windows 8, download Folder association fix from this page. You should be able to start Windows Explorer or File Explorer correctly!