After installing Windows on an HP EliteBook 8570p, you might find that the brightness keys are not working. To fix the brightness keys on an HP EliteBook 8570p, install the hotkey drivers:
http://h20565.www2.hp.com/portal/site/hpsc/public/psi/swdHome/?lang=en&cc=us&sp4ts.oid=5212913
Alternatively, you can adjust the brightness by going to Display in the Control Panel and clicking Adjust Brightness on the left hand side pane. At the bottom of this window, you will see a slider bar called Screen brightness.