If you check ***this thread at the HP forums***
, and that is your problem, it seems to be a problem with the monitor. You didn't say if you were using an HP monitor along with your HP computer -- or if you have an HP laptop.
The ***last post of the same thread***
is by someone saying it was due to bad solder on the monitor connections.
My two cents. I have repaired many monitors over the 40 years I have been in business and what I have found on these very nice HP monitors is bad solder. These are high quality monitors made mostly by LG however the soldering process is a bit flawed. If you remove the front bezel you are able to remove the assembly that has the four push switches. After removing the two screws you may need to carefully bend the rear housing plastic a little to get the assembly to come out. Resolder all the connections on this board, even if they look good they aren't. This should fix the volume, auto adjust and any other crazy pop up. It will also cure some monitors that don't want to shut off. This whole process shouldn't take more than a half hour. I hope this helps.
Lots of people have blamed the computer software rather than the hardware, suggesting everything from reinstalling drivers to reinstalling the whole operating system. Since the problem is intermittent, reinstalling may seem to have worked at first, but according to that thread, the problem always comes back because the problem is in the hardware.