What does the third light from the left indicate?

http://h10032.www1.hp.com/ctg/Manual/c00873752.pdf

The Power light is on, and one or more of the printhead lights blink. One or more of the
printheads are missing.
• Install the
indicated
printhead, and
then try to print.
• If the error persists
after installing the
indicated
printhead, see
Device does not
accept printhead.
• If the error still
persists, replace
the indicated
printhead

From the left - Light 1 is ink cartridge, (color indicates which ink) Light 2 is Print head, light 3 is configuration, 4 is cancel, 5 is resume , 6 is power.
Probably it's out of yellow ink.

Here's the HP page for your printer : http://h10025.www1.hp.com/ewfrf/wc/product?product=2511753&lc=en&cc=ca&dlc=en&submit.y=0&submit.x=0&lang=en&cc=ca

The manual is here : http://h10025.www1.hp.com/ewfrf/wc/manualCategory?lc=en&dlc=en&cc=ca&lang=en&product=2511753&