How to close laptop lid with power on?

There is a time when you want to use an external monitor and you want to close your laptop lid because you don't want to get more dust into your laptop. The following are steps to take:

1. Click Start.

2. Click Control Panel

3. Double click Power Options

4. Click Advanced tab

5. In Power Buttons section, select "Do nothing" at "When I close the lid of my portable computer"

6. Click Ok to finish.