If multiple programs are running in full-screen mode or an open program is covering the taskbar, you may be unable to switch to another program by pressing the Windows key and then clicking the program's icon on the taskbar.
This behavior can occur if the Always On Top check box is not selected in the Taskbar Properties dialog box.
To resolve this behavior, follow these steps:
Press ALT+TAB to switch to another program.
Click Start, point to Settings, and then click Taskbar & Start Menu.
On the Taskbar Options tab, click the Always On Top check box to select it, and then click OK.
Press CTRL+ESC, and then double-click the other program's icon.