Can´t log in to Windows XP Pro

[Pastel]

2 days ago, when I would start my laptop (HP Compaq nx6125), a "Log On to
Windows" window appeared and requires an "UserID" and "Password" I have never
had before. When I used my daughters name as "UserID" and no password, the
system tried to start Windows (and played the starting melody) but a couple
of seconds later logged off (and played the closing melody). Nothing else
worked.
Laurent have had identical problem and Andrew E. sugested "At start up,tap
the F8 key,select safe mode..." My problem is, that F8 doesn´t work, nothing
heppens by pressing it. Only F10 works.
Is there any way out from this problem?
All answers and tips are appreciated...

 

[Pastel]

Now even F8 works, but even in "safe mode" occurs exactly the same problem. I
tried even to reboot Windows from Operating System DVD, without success.