By default the Chromebook will open the Powerpoint in Google Slides and that will not play sounds. 
Google Slides Example

Open the file in Microsoft Powerpoint Online 
Powerpoint Online

Click the Upload and open button at the top of the box showing recent presentations.
You'll be prompted with the location of the Powerpoint file you wish to open.
By default the Powerpoint loads in edit mode, you'll need to select Slide Show from the menu at the top and start the slide show.

The sound files must be activated in Powerpoint Online by clicking on the triple dot menu as shown below:

Keep in mind there may be times where you may need to move the speaker icon in edit mode because the Play menu option appears off the screen otherwise.