Can't System Sounds Working

Sometime my system sounds work and most of the time they don't. My Device Manager doesn't show any problems. When I right click on the sound icon in the System Tray and click on Sounds, then try the sounds, most of the time they don't work. I have all the latest digitally signed drivers (HP Pavilion laptop). When I go straight to the Sounds folder and try the sounds, they don't work. I don't even know which app is supposed to play these sounds (it might help if I knew in order to solve the problem). I have no viruses or malware in my system. Not sure - but it seems like the system sounds stop working sometime while the system is booted and has been running for a while. Please could someone offer some other things to check or try? What app is supposed to run these sounds? Are there any other sites that might be able to help (or other Newsgroups)? I depend heavily on these sounds working properly so thi sissue is important to me to solve. If I've left out any relative detail,