Open up a folder (Documents, Libraries, whatever) and click elsewhere to lose focus (we're doing this to simulate your missing GUIminer window)
In the taskbar, left-click once on the folder icon so it gains focus
Now, press "ALT-Space" (you will see a menu appear on the folder)
Press "M" to choose the Move option (your cursor will now turn into four arrow points).
Press any of the cursor keys once (this will move your folder on the screen and it will be captured by the mouse)
Move your mouse about and you will see the folder moving with it
Left-Click to "drop" the folder onto your desktop