Bios battery/cmos battery. It's the watch battery down by the gpu slot. Old boards are especially susceptible to that being depleted because of age.
But I don't think that's the issue, because if cmos doesn't load at boot, the boot defaults to searching for all available info. Which is what happens after a manual shutdown or reset. Sounds more like there's an issue with what windows is saving to cmos, it being corrupted on save, which can happen with software conflicts, driver version conflicts etc.
I'd suggest using ccleaner (piriform.com free version) and using the tool to clean out your pc. Also use the registry tool (say Yes! to backup) and resort your registry clean of dead ends, conflicts etc.
Also, use start menu - CMD with Admin privileges,
dism /online /cleanup-image /restorehealth
and
SFC /scannow
(be mindful of spacing before the /'s).
That'll start your system out clean, then if the issue persists, you can start looking at other options.