Hi and welcome go Geeks to Go. Are you able to boot into safe mode? Do you have a Windows install (bootable) cd? First, I suggest trying a system restore. Here is info from windows help, starting in safe mode and system restore in insafe mode:
To start the computer in safe mode
You should print these instructions before continuing. They will not be available after you shut your computer down in step 2.
Click Start, click Shut Down, and then, in the drop-down list, click Shut down.
In the Shut Down Windows dialog box, click Restart, and then click OK.
When you see the message Please select the operating system to start, press F8.
Use the arrow keys to highlight the appropriate safe mode option, and then press ENTER.
If you have a dual-boot or multiple-boot system, choose the installation that you need to access using the arrow keys, and then press ENTER.
In safe mode, you have access to only basic files and drivers (mouse, monitor, keyboard, mass storage, base video, default system services, and no network connections). You can choose the Safe Mode with Networking option, which loads all of the above files and drivers and the essential services and drivers to start networking, or you can choose the Safe Mode with Command Prompt option, which is exactly the same as safe mode except that a command prompt is started instead of the graphical user interface. You can also choose Last Known Good Configuration, which starts your computer using the registry information that was saved at the last shutdown.
Safe mode helps you diagnose problems. If a symptom does not reappear when you start in safe mode, you can eliminate the default settings and minimum device drivers as possible causes. If a newly added device or a changed driver is causing problems, you can use safe mode to remove the device or reverse the change.
There are circumstances where safe mode will not be able to help you, such as when Windows system files that are required to start the system are corrupted or damaged. In this case, the Recovery Console may help you.
NUM LOCK must be off before the arrow keys on the numeric keypad will function.
To run System Restore in safe mode
Access System Restore through Help and Support.
Follow the instructions on your screen.
To access the System Restore Wizard, click Start, and then click Help and Support. Click Performance and Maintenance, click Using System Restore to undo changes, and then click Run the System Restore Wizard.
While the computer is in safe mode, System Restore does not create any restore points. Therefore, you cannot undo a restoration that you performed when the computer was in safe mode.
You can use System Restore to restore your computer to any restore point while in safe mode. If you cannot start the computer in standard mode, you can use System Restore to restore to a time when you could start the computer without errors.
To restore to a time when your computer started without errors, select a restore point as close to the time you remember it last started without errors.
If System Restore is suspended because of insufficient disk space, you cannot enable it by making more disk space available while in safe mode. You must restart the computer in standard mode and make more disk space available.
If this doesn't get you going again, you can try booting to the windows install cd and doing a repair install
Here is a guide for that: http://www.geekstogo...ws-XP-t138.html