Here is the driver from A4Tech website for your A4tech PK-635 web camera. Works with Win98, Windows 2000/XP/Vista/Win 7

http://www.a4tech.com/downloads.asp

Put in PK and 635 and then GO, then on the left side click download.

1st You download Webcam Driver.
download the driver
After this install the Webcam driver in the system.
Installation of Webcam Driver
Go to the control panel
Click on the System Icon
Click on the Hardware Tab
Click on the Device Manager s
Select the Unknown Device or printer device where yellow Question Marks sign on it.
Right click on it and uninstall it.
After this go to the top of the device manager and click on scan for hardware changes.
Driver installation Wizard start.
Brows Your Driver from the Hard Disk and click on next.
Driver will be install.

A4Tech drivers are available fromtheir WEB download site - click on this link and select your model WEBcam todownload : -
http://www.downloadatoz.com/driver/item_a4tech-pk-635-webcam-driver.html