It sounds like what is happening it it has an auto sensing headphone jack. When it detects something plugged into the headphone port it automaticly turns off the laptop speakers. Since it's damaged it still thinks something is plugged in. You could try a USB headset and see if it will overide this setting. A USB or PCMCIA sound card may also work if you can disable the onboard one, in the BIOS or device manager.

What model is the laptop?