Reboot your computer, and press F8 until you get to the
option menu, look for "Last Known Good Configuration".
Try that and see what happens.
Also if that does not work, then try Repairing winxp, now
by doing this you will need the winxp cd of course and to
set your first boot device in BIOS to your CD-ROM in some
cases it will say CD-ROM and some others it will be
something like [Manufacturer]And Numbers or Letters.
Example: TDK-124048
Select your CD-ROM and save and exit.
Now when it ask's you to press any key to boot from CD, do
so and press any key.
Now it will examine your hardware and after it should
bring up a blue screen, when this comes up press F8.
Now you should select one of the settings that say as
follows, "Repair your current Installation" something like
that.
Just Press "R"
And let it goto work
Hope that helps.