症状：插上耳机后声音还是从扬声器出来。几天前还好好的。
找了几个方法无效，最后找到这个，照做后成功：
1. Open the Device Manager (type devmgmt.msc in the search box and hit Enter).
2. Expand the "Sound, video & game controllers" and right click on "Realtek High Definition Audio".
3. Select to "Update Driver Software".
4. Click on "Browse my computer for driver software".
5. Click "Let me pick from a list of drivers on my computer".
6. Put a check in the box "Show compatible hardware" if not already checked.
7. In the list of devices, click "High Definition Audio" (the native driver).
8. Click "Next".
9. On the Update Driver Warning box, click "Yes" (install the driver).
10. Restart the laptop if prompted. If not prompted, then no need to restart.