Hi ! I didn't make this post to ask for help, but rather to help whoever has the same issue as me in the future because I managed to solve it.

So I bought this nice Pentium 3 laptop a few months back and it works fine. However upon the first startup, I was greeted with a "CMOS battery dead". Nothing to worry about, right ? Well sure I could boot off of the hard disk drive, so the PC was usable. However once I tried to enter the BIOS to set the time, I was prompted to enter a password. WTF ?! The CMOS was cleared, why is it asking me a password ?

I my first reaction was to google around that issue, and found out I wasn't the only one, over the past two decades I could find people asking what password to enter and people replied with the password to enter right away.

The thing is, you need first to get a hash from your computer, so each computer has a "unique" password. So grabbing someone else's password won't work. And also the people helping didn't explain how they did it, they just did it ... so I had no real solution and each searches lead to the same kind of thing (or people being answered to replace their motherboard, or people having no answers, and most answers being from over 10 years ago).
By the way to get the hash, you need to press F12 when the password is prompted.

So what did I do to solve this issue ? Well I gave it another try and this time I found again the same kind of post, except that one of the answers had a screenshot from a software. So I googled around and found it !

It's actually a open source software !!
You can find it (and many others here) https://dogber1.blogspot.com/2009/05/table-of … eered-bios.html
The one you need is "pwgen-5dec.py"

So I gave it a go, entered my hash into the program, it generated a password. I entered it ... and voilà, I can go into the BIOS !!!
@dogbert, if you ever come here, thank you very much for making these programs !!

So this is how I managed to get rid of that stupid password. If you have the same machine, try this man's program, it should fix your problem 😀 (and if you have another PC with a similar problem it's likely that he has another program to fix that !)