How to disable / enable the internal speaker.

Open Device Manager

In Device Manager click View and click "Show hidden devices"

This should make "Non-Plug and Play Drivers" visible in Device Manager.

Expand Non-Plug and Play Drivers by clicking the plus and double-click Beep.

Within the "Beep properties" window click the Driver tab.

Under the driver tab if you wish to temporarily disable this device click the Stop button. If you wish to permanently disable this device under the Startup Type select Disabled.