Hi,
Thank you for posting your query on Microsoft Community.
As per the issue description A4TECH PK-635G WEBCAM is not working on Windows 10 and the same webcam is working on Windows 7 computer. The issue could be if the drivers of the webcam is not compatible for Windows 10 or the manufacturer of your webcam has not released the driver for Windows 10.
I would suggest you to install the drivers for Windows 78/8.1 from the manufacturer's website in compatibility mode and check if that works.
Make older programs compatible with this version of Windows
http://windows.microsoft.com/en-in/windows-8/older-programs-compatible-version-windows
Reference:
Do keep us updated.
Regards,