Hi,
Welcome to Microsoft community forums and thank you for posting the question. I will surely help you to find a resolution regarding the issue.
1. What is the model number for the Acer laptop?
2. Was it working before?
3. Have you installed the latest drivers for the webcam from the Acer website?
4. Do you have any application programs such as messengers or chat apps installed on the computer to check?
I would suggest you to open any application that uses webcam and enable webcam option in the options. If it is not working, I would recommend you to download it from the website below:
http://support.acer.com/us/en/drivers_download.aspx
Once the driver is installed you can use the webcam on different applications like Chat Messengers etc.
You may also download check the user manual from Acer on about how to turn on the camera.
In the link below browse to the notebook model and click on "Document" tab and you can download the e-manual of the notebook.
http://support.acer.com/us/en/drivers_download.aspx
Also refer:
Seeing is believing
Hope this information helps. Please reply with the status so that we could help you further.