Most systems today handle this via the BIOS -- that cryptic note saying
"Press (Del/F1/F2/whatever) to enter system setup" while powering up.
Once in the BIOS setup there is usually a security section where you can
enter a password that comes up when you power up the machine.
This means, no password, no boot and no forgiveness. You forget the
password, you can forget using the system. However, the motherboard
should have a jumper that you can set that blanks the password for just
such occasions. You'll have to check your motherboard doc. So while
the mechanism to break in is simple, they do make you work for it.
If any of this is confusing or puts you off, get someone with a bit more
experience to handle the job. There a million ways to hose your system
in the BIOS setup program.