It certainly sounds like you have a BIOS password set. It could (very, very
rarely) have happened spontaneously by a power surge but usually it is done
by a human being. When I taught computer tech some naughty students used to
put BIOS passwords on the computers. It was a game for them, but a real
inconvenience for us until I found Kill CMOS.

There are two solutions. You can take the case off and find the jumper to
clear the CMOS settings. There are several variations but usually you either
put a jumper on or remove it and it flushes everything back to the default
settings - including no password. A more elegant solution is to use a
utility such as "KillCMOS", which easily fits on a floppy disk. It is
bootable and contains code that resets the BIOS to it's defaults - again
with no password. You can find it here
http://majorgeeks.com/download.php?det=2969 . You will need another computer
to make a bootable DOS boot disk and copy the killcmos file onto it. Then
just insert the diskette, start the computer and watch it happen.

If by any chance the computer in question has no floppy drive it should work
just as well if you prepare a bootable CD or DVD with the same tiny (8 Kb)
file on it. One caution. Any Anti-virus software that is any good will tell
you this little programme is a virus. It's not, but it does what some
viruses do, which is what you want in this case. Keep it on a floppy disk,
because your computer's anti-virus software may "clean" it and render it
useless.