A4tech black or blank screen problem

Test your webcam here, by hitting "allow" in top window and assess your cam in left panel.
If it works there you know the Hardware is ok (webcam/lead/USB etc)
Test it in Yahoo
Re-boot the webcam by unplugging it from the USB and plugging it back in again
Open Messenger - Click (>) Messenger > My webcam > OK
Your webcam should launch - if it fails to do so you have a software problem.
Try updating your driver from the Imaging folder in Device Manager
Expand the folder, right click on your webcam text and select "Update driver" opt for Internet, when prompted.
No luck ?
Uninstall webcam software from Programs.
Restart computer
Go to A4Tech website and download software
http://www.a4tech.com/ennew/support.asp

Once your webcam is working on your computer,you can configure it to Yahoo Messenger.
Its good practice to disconnect and re-connect your webcam before you start - if you have been using it elsewhere the Yahoo software may have difficulty in locating it. Mine, I just unplug it from the USB and plug it back in,

INTERNET CONNECTION
Webcam connected
Open messenger - on top toolbar. Left click ( > ) Messenger > Preferences > Connection - Select 'no proxies' or 'connect direct to the internet' depending on the version of messenger you have
make sure your internet connection and country are correct in the lower two boxes > Apply > OK

TESTING
> Messenger > My webcam - the warning panel will launch, click 'OK' and your webcam will start. You should be rewarded at this stage with your happy smiling face.

DEFAULT
With webcam still running > Messenger > Preferences > Webcam > Camera Source - set your webcam as default using dropbox. > Camera Settings - adjust settings to suit. > Apply > OK
Take a note of any additional software, if you have multiple choice for Camera Source, you may wish to uninstall any redundant webcam software later to prevent conflicts