Audio from headphones is muted after screen is locked or sleep mode (Windows 8.1)
Since this topic is over two years old and no 'answer' has been provided, I'm happy to collect the points. Here is the answer that the author found, his/her self (moved here from the question).
This is the weirdest thing ever happened to me. Here's what I found out:
By itself the audio driver (be it the default "High Definition Audio" from Microsoft or "VIA HD Audio(Win8.1)" from VIA) stops sending the sound to line-out after waking up from sleep mode
If I also execute the hot keys manager from CLEVO (HkeyTray.exe) audio works through suspend/wakeup but doesn't work after locking the screen
Now the best! Inside the hot keys manager's folder (in my case C:\Program Files (x86)\Hotkey) there is a small .exe file called InitHeadphone.exe. As you can guess running it re-enables audio from line-out/headphones no matter what you did (sleep, lock, whatever). It seems to have some dependencies so it must be run inside the folder.
What an adventure folks! I'll try to investigate more and understand why there is such a connection between two pieces of software of two different producers (CLEVO and VIA). It's almost like they are in a symbiotic relationship! I hope this will help somebody. Please let me know if so. :)
Temporary Workaround
If your headphones/Line-out don't work after sleep mode or locking the screen and you have a VIA sound card just download CLEVO's hot keys manager and run the file initHeadphones.exe. I still have to figure out why though...
Stable Solution
wspawn from the forum of Notebook Review (thank you! You are still welcome to post an answer yourself) found the following solution:
To prevent the hotkey software from messing with the audio controls / headphones rename the following file: C:\Program Files (x86)\Hotkey\hp.dll to C:\Program Files (x86)\Hotkey\hp_DISABLED.dll.
FINAL SOLUTION
Apparently installing the Hotkey utility from CLEVO (which can be also found on Sager's drivers page) is enough. Latest version is 8.0100. I still have to find a way to fix the problem without installing this stupid program.
As an addition to Reeves's answer, it is possible to solve this problem without having Clevo's hotkey program running.
Note that, as far as I'm aware, this problem is unique to Clevo laptops, but affects a huge number of them. It is a bit annoying that this problem has existed for years, but Clevo seems perfectly happy with their software hack to fix the (presumably) hardware bug.
On Windows
What we need to do is run the InitHeadphones program every time the computer wakes from sleep.
First, one does unfortunately have to first install Clevo's Hotkey program, as explained in Reeves's answer to get the InitHeadphones program. If there is an easier way, please correct me!
Second, disable the Hotkey program from autostarting.
Finally, open Windows's Task Scheduler application. Set the action to run InitHeadphones.exe (By default, C:\Program Files (x86)\Hotkey\InitHeadphones.exe) and the trigger to be:
Begin the task: On an event Log: System Source: Power-Troubleshooter Event ID: 1
On Linux
There exists a project called init-headphones on Linux, which provides a Python program which talks directly to the amplifier and tells it to behave.
Link to repository: https://github.com/Unrud/init-headphone
This program does exactly what it says on the box with no hassle after being set up