Hi and Welcome!
Either your sound hardware went bad (It would be good if your computer were still under warranty then), or it's just a Windows or driver issue.
How do i fix it??
Unfortunately, you did not mention the brand of your laptop. If it's a Dell, then run the built-in Diagnostic utility. I have no idea if other brands offer such tools also.
Alternatively, you can get a Live Linux CD like Ubuntu or Sidux and check if the sound is still bad if booted from such a CD.
In case it's the hardware, either contact manufacturer support to have it fixed, or buy a USB audio device. The latter is the much cheaper option if warranty is already expired.