salam dear Omani2

i don't have arabic font so i will write in english ... so sorry for that
try to follw this step

if it's not clear ask me ... Ok

Cause: Yahoo! Chat is unable to locate the DSP Group TrueSpeech audio compression (codec) software on your computer.
Solution: The DSP Group TrueSpeech audio compression (codec) software is usually installed as part of Microsoft Windows. Please follow these instructions to install and enable the TrueSpeech codec (make sure you select the correct set of instructions depending on whether you are using Windows 95, Windows 98, or Windows NT):

Follow these instructions if you are running Windows 95 or Windows 98:

Press the Start button in the lower left corner of the screen.
Select Settings, then Control Panel.
Double-click the Multimedia icon. The Multimedia Properties window should be displayed.
Click on the Advanced tab.
Click on the plus-symbol (+) next to Audio Compression Codecs to expand the list of installed codecs.
If DSP Group TrueSpeech(TM) Audio CODEC is displayed, go to step 18.
If DSP Group TrueSpeech(TM) Audio CODEC is not displayed, it needs to be installed. You will need your Windows CD-ROM (or will need to locate the Windows installation files on your computer).
In the Control Panel window, double-click the Add New Hardware icon. The Add New Hardware wizard should be displayed.
Press the Next button.
You will be asked if you want to search for your new hardware. Select No, then press the Next button.
Select Sound, video, and game controllers from the Hardware types and press the Next button.
Select DSP Group from the Manufacturers list and TrueSpeech(TM) Software CODEC from the Models list, then press the Next button.
Press the Finish button.
You may be prompted for the location of your Windows CD-ROM. Enter the correct location and press OK.
You will be prompted to restart Windows. You may restart now or later, but the codec will not be available until you restart your computer.
If, after restarting your computer and attempting to start a voice chat, you are still receiving the same error message, continue to the next step.
Open the Multimedia Devices window as directed in steps 1-5.
Select DSP Group TrueSpeech(TM) Audio CODEC from the list of Multimedia Devices and press the Properties button. The Properties window is displayed.
Verify that Use this audio codec is selected and press the OK button.
Press the OK button in the Multimedia Properties window and try using voice chat again.
Follow these instructions if you are running Windows NT or Windows 2000:
Press the Start button in the lower left corner of the screen.
Select Settings, then Control Panel, then Multimedia. The Multimedia Properties window should be displayed.
Click on the Devices tab.
Click on the plus-symbol (+) next to Audio Compression Codecs to expand the list of installed codecs.
If DSP Group TrueSpeech(TM) Audio CODEC is displayed, go to step 13.
If DSP Group TrueSpeech(TM) Audio CODEC is not displayed, it needs to be installed. You will need your Windows CD-ROM (or will need to locate the Windows installation files on your computer).
Press the Add button. The Add window should be displayed.
Select DSP Group TrueSpeech(TM) Audio CODEC from the list of drivers, then press the OK button.
If the Driver Exists warning is displayed, press the Current button.
You will be prompted to restart Windows. You may restart now or later, but the codec will not be available until you restart your computer.
If, after restarting your computer and attempting to start a voice chat, you are still receiving the same error message, continue to the next step.
Open the Multimedia Devices window as directed in steps 1-4.
Select DSP Group TrueSpeech(TM) Audio CODEC from the list of Multimedia Devices, and press the Properties button. The Properties window is displayed.
Verify that Use this audio codec is selected and press the OK button.
Press the OK button in the Multimedia Properties window, and try to start a voice chat again.