Use your original recovery CD, and follow the instructions for a repair install:
XP Repair install
Please read carefully and make sure you followed the warning links before initiating the Repair Install. You can print a text version for reference. repair.txt
Boot the computer using the XP CD. You may need to change the boot order in the system BIOS so the CD boots before the hard drive. Check your system documentation for steps to access the BIOS and change the boot order.
When you see the “Welcome To Setup” screen, you will see the options below
This portion of the Setup program prepares Microsoft
Windows XP to run on your computer:
To setup Windows XP now, press ENTER.
To repair a Windows XP installation using Recovery Console, press R.
To quit Setup without installing Windows XP, press F3.
Press Enter to start the Windows Setup. do not choose
“To repair a Windows XP installation using the Recovery Console, press R”, (you Do Not want to load Recovery Console). I repeat, do not choose “To repair a Windows XP installation using the Recovery Console, press R”.
Accept the License Agreement and Windows will search for existing Windows installations.
Select the XP installation you want to repair from the list and press R to start the repair. If Repair is not one of the options, END setup. After the reboot read Warning#2!
Setup will copy the necessary files to the hard drive and reboot. Do not press any key to boot from CD when the message appears. Setup will continue as if it were doing a clean install, but your applications and settings will remain intact.
If you get files not found during the copying stage.
Blaster worm warning: Do not immediately activate over the internet when asked, enable the XP firewall before connecting to the internet. You can activate after the firewall is enabled. Control Panel - Network Connections. Right click the connection you use, Properties and there is a check box on the Advanced page.
KB 833330u Blaster removal
What You Should Know About the Sasser Worm and Its Variants
Microsoft Security Bulletin MS04-011
Reapply updates or service packs applied since initial Windows XP installation. Please note that a Repair Install using an Original pre service pack 1 or 2 XP CD used as the install media will remove SP1/SP2 respectively and service packs plus updates isssued after the service packs will need to be reapplied.
see: http://www.michaelstevenstech.com/XPrepairinstall.htm
It should have been mentioned that the computer uses Windows 2000 professional, and this is being typed on another computer--how can the computer be checked for viruses and chkdsk be run with the computer being nonfunctional?
Which leads to to the next point: it almost can't be emphasized enough that not an expert on computers, so if the instructions could be given as though you were typing to an idiot, that would be helpful.