This is not an XP issue. If you have a desktop machine, refer to the
motherboard manual. There may be a simple jumper setting that clears CMOS
or you may need to remove the motherboard battery. Removing the motherboard
battery and letting the computer sit for some time (sometimes a few
minutes, sometimes hours) will reset the CMOS back to default (no
password).
If you have a laptop, contact the laptop mftr.'s tech support for help.
Removing the battery could/might solve it,but remove it,locate the CMOS
jumper pin on the board (usually by the battery),move the pin from 1-2 to
2-3 position for .45 seconds or so,then back to 1-2 position,replace battery,
start pc.You'll need to enter & reset the BIOS before xp will load
(date/time,etc).