Instructions
Click the "Steam" button in the top left hand corner of the client screen. Alternatively right click the "Steam" icon situated to the left of the system clock on the bottom right hand side of your Windows screen.
Click the "Exit" option. The Steam client will close down.
Double click the "Steam" icon on your Windows desktop. Alternatively click the Windows "Start" button then click the "Steam" icon from the menu.
Enter the username and password associated with your Steam account to log back into Steam.