First check the audio buttons on your laptop to make sure the sound is not too low or muted. I sometimes clumsily forget that some FN key + audio button disables audio too. Have you tried your laptop with other headphones? If the same problem occurs, it is likely your audio drivers stopped working.
If you have an audio driver problem, try searching for one on lenovo's site:
https://pcsupport.lenovo.com/us/en/products/laptops-and-netbooks/lenovo-n-series-laptops/n21/downloads