Since you don't have an XP CD, download and create a bootable CD from the .iso file
XP Recovery Console
You don't burn the iso file itself to CD., you create a CD from the iso file using your CD burning software. I use Roxio but Nero or Ahead InCD will also work. There is a good freeware burner called
DeepBurner which will do this. Another called
ISO Recorder is also very easy to use.
Boot the CD and at the first opportunity, enter
R to start the Recovery Console.
Next, choose which XP installation you want to login to. Normally this will be 1.
Lastly you will be asked for the Administrator password. Just press the Enter key as the Administrator does not have a password (unless you gave it one, then you would enter it).
From the command prompt, enter:
chkdsk c: /r
It can take an hour or more depending on the size of the hard drive.
Allow it to complete undisturbed.