Generally, the first step is to test with a second application that supports webcams. Skype, or Yahoo Messenger or one of many other apps you might have installed with webcam support. If that works, then it indicates there's a problem with a particular application. If it fails, that means you have a problem with the camera (hardware) itself or the camera drivers.
If that test confirms the problem is with a particular application contact the app vendor (this could be ArcSoft) and explain that the app isn't working but you have confirmed that the camera itself is fine and list which applications prove it's working.
If the initial test shows that all apps fail, the easiest thing to try is reinstalling the camera drivers. If you aren't sure how to do that, contact the camera vendor.
If you've reinstalled the drivers, and the camera still doesn't work, it's possible the camera hardware itself is broken, but it might still be worth contacting the hardware vendor and letting them confirm whether or not they agree that's the case.