You have tested the system with a headset? Since the external audio connection is normally on the motherboard, if it were to work, then there is a possibility the speaker connection was unplugged during the screen replacement.
I suppose for any function key combinations that would enable or disable the audio should be checked, it you have not already.
sorry for taking so long to reply. No system recovery. You are not in the bios. You hit F8. It will be either F1 F2 or Delete button on the first screen you see after pushing the power button.
Do this instead go to control panel click on Hardware and Sound. Then under sound last option "Manage audio devices". On the window that pops up you will see a Speaker icon. Highlight it and at the bottom of the window click on the properties button. The next window that appears at the bottom is Device usage:
Make sure the device is enabled in the drop down.