1.Check for other buttons on them.
2.Unplug , restart, and plug them again.
3.Check Volume on your PC.
4.Check Sound and audio devices in Control panel under Volume tab and under the Speaker settings (check volume , set speaker type in Speaker setup, etc)
5.See if sound card is detected in Device manager and try updating your sound card from manufacturer site.
6.Somethimes U may need to chipset drivers also for sound to work.
7.See if Windows audio selected in Start>run> msconfig> services.
8. See bios settings (only if needed)