If you can view the TV picture but get no audio, you should check the following:
For digital broadcast, please check that the WAVE sound is not muted or volume too low in the Windows Volume Control dialog. (Double-click on the speaker icon in the system tray.)
For analog VCR capture (T300 only), check that it is connected between the internal Audio-Out of the TV tuner card and AUX-In or CD-Player of your sound card and that you selected the audio source to “AUX or CD Player.”.
Also check that the sound is not muted or volume too low in the Windows Volume Control dialog. (Double-click on the speaker icon in the system tray.)
Sometimes updating the sound card driver from vendor or TV card's driver and application may help as well.
If above doesn't help, please update product sofware and your sound card driver.
VideoMate DVB-T300 can enable PCI audio which is TV sound can go through PCI interface without connecting audio patch cable. Please try to use it by check the PCI Audio checkbox in the System Device in Settings of ComproDTV.