Not sure what's going on, but you can try this as a workaround. Open Task Manager by pressing Ctrl-Alt-Delete and then clicking Task Manager. On the Processes tab of Task Manager, click the process "explorer.exe" and then click End Process.
The taskbar and your desktop icons should go away completely. In Task Manager, click File and then click New Task. In the Create New Task window, type "explorer.exe" and then click OK.
This should bring your desktop back. You can also restart the computer from that security screen you see when you press Ctrl-Alt-Delete.
As far as why this is happening, has it happened before? Did it happen right after your computer started or had your computer been running for a while?