2. Right-click on My Computer-Properties-Hardware-Device Manager to see if there is a yellow "?" In front of the equipment. Or "!" . If so, please reinstall the driver for this device.
3. When you can't see the speaker in the lower right corner, open the control panel-Audio-Video Equipment-Volume, and put a tick in front of "Put the volume icon in the taskbar".
4. Reinstall or upgrade the sound card driver. There is a sound card driver on your motherboard driver disk. If you can't find the driver, you can download the driver wizard and update the sound card driver. It will automatically identify the driver, automatically install it, and it is the latest driver.
Sometimes, you can get back to normal by restarting your computer. I have tried many times, but I don't know why it will return to normal.