Hello and welcome to the forums. Acer's website, support and download center would probably be a good place to start most likely they would have a driver for the ethernet controller as well as the modem driver that you are evidently missing.
We can try to help if you will provide the hardware ID for the device. Try opening device manager again, right click the problem device choose properties, select the details tab, change the property value drop down arrow to Hardware IDs then in the value box, right click and choose select all, then right click again and choose copy. Then paste that information into your next post and we'll see if we can find any help for you.