i use CAMTASIA . however i can't record video. it's always appear blank. but the sound is ok. please help.

Answer 1

First off if the application your trying to record makes use of hardware overlay, Camtasia (or any other video capture software i know of) will not be able to capture the images you see, it will instead capture to a mask colour (usually black).

This problem is documented at the Camtasia support site and it will tell you exactly what i have just told you with more detail.
http://techsmith.custhelp.com/cgi-bin/techsmith.cfg/php/enduser/std_alp.php

Not sure the direct link will work but here it is
http://techsmith.custhelp.com/cgi-bin/techsmith.cfg/php/enduser/std_adp.php?p_faqid=27&p_created=1102520833&p_sid=coh4jUwi&p_accessibility=0&p_redirect=&p_lva=&p_sp=cF9zcmNoPSZwX3NvcnRfYnk9JnBfZ3JpZHNvcnQ9JnBfcm93X2NudD02NDEmcF9wcm9kcz0mcF9jYXRzPSZwX3B2PSZwX2N2PSZwX3NlYXJjaF90eXBlPWFuc3dlcnMuc2VhcmNoX25sJnBfcGFnZT0x&p_li=&p_topview=1

It also says the following might help (be cautious though):
The best solution is to disable hardware acceleration in the application that is playing the video or disable hardware acceleration system wide. Because this affects all applications on the system, it may cause performance problems for some applications and some applications may not run at all.
How to disable graphics hardware acceleration globally for all applications:

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Windows XP or 2000: Right-click on the desktop and select Properties > Settings > Advanced > Troubleshoot. Set the Hardware acceleration slider to None.
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On other versions of Windows: Select Control Panel > System > Performance tab > Graphics > Advanced settings. Set the Hardware acceleration slider to None.

How to Disable Hardware Acceleration:

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Windows Media Player: In Media Player 10, select Tools > Options > Performance. In Media Player v6.4 and earlier, select View > Options > Playback. In both cases, slide the Hardware Acceleration slider to None.
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RealPlayer: From the Tools menu, select Preferences > Hardware and set the Video Card Compatibility to Most reliable by moving the slider all the way to the left.
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RealPlayer G2: Select Options/Preferences from the RealPlayer menu. Go to the Performance tab and disable (uncheck) the Use optimized video display setting. You may need to close and restart RealPlayer G2 to have the change take effect.
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Apple QuickTime: Select Edit > Preferences > Streaming Transport. In the dropdown box, select Video Settings and uncheck all of the DirectDraw options.
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Flash Player: None.

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Hope that helps