Hello. The problem is either a hardware failure or in the software/configuration. The only way to know for sure if it is the hardware is to perform a system recovery. Doing that will fix any software issues so any problems that remain are due to hardware failure.

Short of performing a recovery, you can:

> Use Windows System Restore (type system restore into the Windows search box) and try to find a restore point dated before the issue began, and return the system's configuration to that date. Doing that will sometimes fix an audio problem.

> Download and install a fresh copy of your Realtek audio driver for the Inspiron M731R model with 8.1. Doing that will fix any corrupted files in the driver and will also fix any user configuration issues.

> Switch to the Windows native audio driver and test with it.

1. Open the Device Manager (type devmgmt.msc in the Windows search box).
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.
[To get back to the Realtek driver,  do it again but reverse the names in steps 1 and 6.]

If there is no audio even with the native driver there is a good chance of hardware failure. As stated above only a system recovery could say for sure. Contact tech support for repair if under warranty.