I can hear sound using ear phones on my HP Pavilion A6603w but cannot hear sound when removing ear phones.

Go into your audio setup, usually the part where it lets you test the speakers (right left front back etc.) there might be a selection in there to turn off the speakers when the head phones are plugged in, uncheck it. This just recently happened to me with a Creative X-Fi audio card, I had never had a card before with that setting and even with the phones unplugged the speakers would not work until I let both work at the same time.