Headphone splitter not working on pc

Hello there.

Have you acticated the microphone in Recording Devices? Right click on the Sound Speaker -> Select Recording Devices -> Select micriphone -> Right click and select as default device

If it doesn't work, then the Sennheiser need a custom adapter. You cannot use simply those startech.
You will need the original PCV05 or PCV07:
https://www.amazon.com/Sennheiser-PCV-05-Combo-Adapter/dp/B00IM36VU0
 
Solution