This seems that someone has deleted ntldr by mistake.
This error occurs when the partition marked as active does not contain the operating system boot files.
Two Issues.
1. Having the PC boot from the correct drive, properly partitioned with the boot partition set as "Active".
2. Having the right files in that partition.
You can change the active partition using fdisk. And you can change the first boot device (but using an optical drive with a Windows CD to boot from can cause you problems later) in the BIOS.
Using Fdisk.
1. Boot to a command prompt by using a boot disk (if you have one. Otherwise you can make one from any Windows 95/98/ME PC.
2. At the command prompt, type fdisk, and then press enter.
3. Click set active partition, choose the partition that you want to make active, and then hit enter.
4. Press Esc.
5. Remove the boot floppy disk, restart the computer.
The below information is from Microsoft.
If the NTLDR is missing or damaged try the Recovery Console.
To start the computer and use the Recovery Console to replace the boot sector
"Insert the Windows XP Professional Setup CD-ROM into the CD-ROM drive.
Restart the computer. If prompted to press a key to start the computer from the CD-ROM, press the appropriate key.
When the text-based part of Setup begins, follow the prompts. Press the R key to repair a Windows XP Professional installation.
If you are repairing a system that has more than one operating system installed, from the Recovery Console choose the Windows XP Professional installation that you need to repair.
Note
If you press ENTER without typing a number, the Recovery Console quits and restarts the computer.
When prompted, type the Administrator password. If you do not have the correct password, or if the security database for the installation of Windows XP Professional that you are attempting to access is corrupted, Recovery Console does not allow access to the local disks and you cannot replace the boot sector.
To replace the boot sector, at the Recovery Console command prompt, type: fixboot [drive:]
Regards Jase