It’s possible they had a dead BIOS battery, and whenever they had to boot up, they had to reset the BIOS clock, or the system would go haywire thinking it was Jan 1, 1992 or whatever the default date was.

I'm not sure, but since it sounds like they opened the BIOS just to close it and boot normally, I would assume that they thought of it more as a command than an option.

I've seen it a lot since I work in an IT field. Sometimes people think that the computer is telling them to do something when really it's just giving the option to do something.

Dead CMOS, or the boot order was wrong and they didn't know how to fix it would be my guess.

Could be a dead CMOS battery, but if the computer had a case switch more likely it was a security feature that lets you know the case was opened. On Acer computers you would have to press F1 to continue the boot, or Del key to enter the BIOS and have the chance to change the setting. Incidentally the setting is usually under the Security tab> Open Chassis. You can reset the notification or turn it off.

I run into this situation on office computers all the time, because no one knows how to turn it off or reset it.

My assumption is that the default boot device was wrong and they needed to go to the bios to switch it but would never save the correct order so they had to do it every time.

Not sure! However, it's possible the coin cell that keeps the BIOS settings was removed or dead. This forces the BIOS into default configuration on boot, which may have caused a boot failure if you needed some specific hardware configuration set in BIOS.

Maybe they used it as a way to control computer access, but it seems more likely that they just didn't get around to replacing the coin cell :D

I'm old enough to remember having to do this myself. Unfortunately I'm also old enough to have completely forgotten why.

It was possible to set a bios password. They might have done that to prevent you from booting the computer without permission.

wrong default boot drive

Your parents werent computer smart people.

Couple of things - back then, bios was slow to load. Add to that if they had a usb keyboard or mouse, the bios wouldn't detect it and make you go into bios (even though the keyboard and mouse it just didn't detect accepted the keypresses to go into bios). There was an option to set in most to skip keyboard and mouse errors. They probably didn't know how to set it.

Are you sure it was BIOS, and not just the password unlock, or they had DOS amd Windows Dual boot?

They had some BIOS issue or wanted to boot from a different partition. Possibly to keep your virus laden downloads away from their files.

I vaguelly remember around this time some low end computers were shipped with FreeDOS instead of Windows, in order to save on licencing fees. AFAIK this was the case because legislation in some european countries restricted the sale of new computers to ones which had an OS preinstalled.

Maybe XP was installed after the purchases however a partition with FreeDOS/whatever remained as the default boot option. Hence your parents had to select the other boot option (Windows XP) manually. Granted you could change your primary boot partition permanently, but maybe your parents didn't know this.

Maybe they didn't setup the boot disk properly? Another explanation could be that some pre-xp pc's required you to type "win" in the CLI for Windows to start it's GUI.

Unrelated, but I remember that my dad had to open up the PC and install a new video card once so that I could use Paint.

Home PCs weren't a thing when my parents were growing up :)

At a guess though, the battery on your motherboard was flat, and the motherboard was throwing a warning whenever you turned the machine on. That was a common issue

I am confident my parents did not do that.

Bios was not set up correctly, or it did not detect the keyboard and was set to fail into bios in that case.

There was no real standard of behaviour that was adhered to for early PCs, so different hardware acted very differently. Standards that were adopted like USB were often implemented in incomplete or incompatible ways.