If you want to lock your Windows workstation there are a couple of different key combinations you can use. You can also create a shortcut and pin it on the Windows 7 Taskbar.
First right click the Desktop and select New >> Shortcut.
In the Create Shortcut window type: Rundll32.exe User32.dll,LockWorkStation. Click Next.
Give the shortcut a name like Lock Computer and click Finish.
The Lock Computer icon appears on the Desktop. Right click on it and select Properties.
In the Properties window select the Shortcut tab. Click Change Icon.
Now type: C:\Windows\System32\imageres.dll into the Look for Icons in This File field. Select the icon you want to use for the shortcut and click OK.
Set the Run dropdown menu to Minimized, then click OK.
Then drag the Lock Computer icon you just created to the Taskbar and pin it.
Now you can click the icon to lock your computer.
If you’re a keyboard master, use [Ctrl][Alt][Delete] then select Lock Computer. Or you can use [Windows Key][L].