You should be offered something like
You'll be prompted for the password. This is the password set for the default administrator account at the time Windows was originally installed.
I found something to try at http://www.computerh.../ch000465.htm#b
, and if it works will be quick and easy to get you back up and running.
Insert the Windows XP bootable CD into the computer.
When prompted to press any key to boot from the CD, press any key.
Once in the Windows XP setup menu press the "R" key to repair Windows.
Log into your Windows installation by pressing the "1" key and pressing enter.
You will then be prompted for your administrator password, enter that password.
Copy the below two files to the root directory of the primary hard disk. In the below example we are copying these files from the CD-ROM drive letter "E". This letter may be different on your computer.
copy e:\i386\ntldr c:\
copy e:\i386\ntdetect.com c:\
Once both of these files have been successfully copied, remove the CD from the computer and reboot.
Let us know if this worked or not. Good luck.