Black Screen We can see our picture on our computer, but when we try to video conference, all the other person sees is a black screen.

Restart your computer and then press and hold F8 keys until you get Advanced Options menu screen.Use the arrow key to highlight Safe Mode, and then press Enter, your computer will boot automatically to safe mode.
If you able to start in the safe mode then Scan your computer for viruses. Some viruses can cause a black Screen , especially ones that infect the master boot record (MBR) or boot sector.
Update drivers for your hardware. black Screens are hardware or driver related so updated drivers could fix the cause of the STOP error.
Return BIOS settings to their default levels. An overclocked or misconfigured BIOS can cause all sorts of random issues, including black screen.
If it didn't helps you then simply get the system utility program like PC Fresher that will fix windows errors that cause of black screen screen

Most like just burned out and needs repaired or replaced.

your laptop is sending video through the hdmi/sata instead of to your laptop screen. Usually when you unplug the hdmi cable it will automatically revert. You have 2 options. One you can hook back up to your tv and use that as a monitor to go into your display settings and reset your laptop screen as the default. Second, you can start up the computer in safe mode and then change the display settings back to the laptop screen as the default. If you get into safe mode and you still dont see anything then the problem is most likely your laptop screen itself has gone and this is all just one big coincidence.

Hook a monitor to the video output, if picture is okay the problem is in the inverter board located just below the screen, or the backlight is faulty. Now if both show the same symptom it is the video graphics chip.

I think you find your answer by going into youtube.com. There a lot of video on doing this type of repair and it somewhat simple too.
How to fix or troubleshoot blank or black screen not powering up issues...

Please check whether you are using web-cam capable software. Ads by Google
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When i connect the other end successfully(all the blue balls color turned to green)but with only a sentence, says:"secure conference encryption 。。。"

I have looked into this for quite some time...what if you get a lot more features in another software...!!! ooVoo is the software and you can use 6 people video conference with recording facility. The problem is Windows Live messanger has some technical issues when it comes to multiple video conferencing...hence ooVoo is for you. Download from here..http://oovoo.com/ there's a free version and trial version giving you full access for 30 days...no credit card required. There are other softwares but they are cheap stuff...so I suggest you to go for this one.

Try this - http://www.darntoothysam.com/
I recommended this to one person who obviously has a bad attitude and just wrote that it was "inappropriate" and spam. I assure you it's not spam and the guy I spoke to had a very good attitude. I sent my camera to them for repair. I hope they can help you.

u reinstall u r drivers try 2 update it
if problem persists contact dealer