I'm presuming you were running chkdsk (not scandisk in XP) on the drive that Windows is installed in - C: drive. If so,
Insert your Windows XP Pro CD and restart your computer.
At the "Welcome to Setup" screen, press F10 or press 'R' to repair.
After the Windows Recovery Console starts, you receive the following message:
Microsoft Windows(R) Recovery Console
The Recovery Console provides system repair and recovery functionality.
Type EXIT to quit the Recovery Console and restart the computer.
1: C:\WINDOWS
Which Windows Installation would you like to log on to
(To cancel, press ENTER)?
Enter the number for the appropriate Windows installation.
Windows will then prompt you to enter the Administrator account password.
Note: If you use an incorrect password three times, the Windows Recovery Console quits. Also, if the Security Accounts Manager (SAM) database is missing or damaged, you cannot use the Windows Recovery Console because you cannot have correct authentication.
After you enter your password the Windows Recovery Console starts.
Type in the following:
chkdsk /r
There is a space after chkdsk
Let it run.
After you've finished what you want to do, type 'exit' to restart the computer.