You have to customize context menu for drive letters.
A Context Menu is what you see when you click the right mouse button on a drive, folder, file, application titlebar, or nearly any other object on the screen. Most of the time, this menu includes a list of actions appropriate to the object on which you've clicked.
Select Folder Options from the Tools menu in My Computer or Explorer, and click the File Types tab.
Highlight the Drivefile type, and click Advanced.
You can add new items, change the default action, and remove unwanted items here. Click Browse and find explorer program in Windows folder. select and approve it, specify it as the default action.