I can only listen to sound on my acer laptop using ear phones but the inbuilt sp

are you sure you did not mute your onboard speakers or reduce the volume of your onboard speakers to zero? remember that you can have different volume levels for headphones and onboard speakers depending on the software you use.

or perhaps there is an actual problem with your built in speakers. they could have a faulty connection or be burned out.

Make sure you have the correct and latest drivers for your sound card. I hade the same problem with my laptop but it was fixed when I installed the correct drivers.