Tried to sign on the computer and I get a black screen that says ntldr is missing; press ctrl alt del to restart. Doing that just gets me back to the black screen. What do I do?

Depending on your situation, below are some things to consider

NTLDR is missing
Simple "ntldr is missing" fix with boot floppy, CD-R, or USB flash

Lot of reading above, you can try the steps above or you can do a repair installation -

Repair Installation
A Repair Install will replace the system files with the files on the XP CD used for the Repair Install. It will leave your applications and settings intact, but Windows updates will need to be reapplied.

Perform a Repair Installation

You need to perform a Repair Installation Method. You will be needing the Windows XP installation disc.

Just follow this steps:

1. First you need to configure the 1st boot device priority of your computer to CD/DVD ROM Drive. You can do that in the BIOS setup.

2. Insert the installation disc and then restart the computer.

3. When the Press any key to boot from CD message is displayed on your screen, press a key to start your computer from the Windows XP CD.

4. Press ENTER when you see the message To setup Windows XP now, and then press ENTER displayed on the Welcome to Setup screen.

5. Do not choose the option to press R to use the Recovery Console.

6. In the Windows XP Licensing Agreement, press F8 to agree to the license agreement.

7. Make sure that your current installation of Windows XP is selected in the box, and then press R to repair Windows XP.

8. Follow the instructions on the screen to complete Setup.

Hope this one helps. :-)