How to cancel a repair re-install?


Hope someone can help me! My friend brought their Dell Dimension round with a problem that it wont boot up. The error message was:
Windows could not start because the following file is missing or corrupt: \WINDOWS\SYSTEM32\CONFIG\SYSTEM"

So I thought I would repair the XP OS using my XP Disc. I booted up from my disc and skipped the recovery console to repair via the reinstall method. All went well until I got to the enter product key section when I entered the key from the label on the PC. It said invalid key so I tried my product key with my disc and again got the same message. (both keys are purchased keys). The OS on the Dell is media center but my disc is XP Pro.

Every time I start the pc now it goes into the reinstall and then of course goes to the product key section. Can i cancel this so I can get back to the original problem?

Can anyone help??
You will need thier disc with their serial. Being that you only have a XP Pro disc and their serial it will never work. Even trying to use your disc with your serial it wont work cause they have MCE. It is a advanced version of XP Pro.

Sadly now that you started teh re-install there is nothing you can do but finish it. PArt of the hardware profile along with some other vital Windows files are now gone and have to be replaced. So even if you could cancel this repair. You would be left with many more problems than before. Have to get a hold of a MCE disc.
Ok so I got a WMCE disc and tried to load that but it stops and says the product catologs are not loaded and quits. If I try to load from disc it says the signature is wrong. Any ideas?
Sounds like the disc is corrupted. It is either that or the disc is missing something that Dell put on their disc. But to me it sounds like a bad copy of MCE.
Looks like the repair is sunk, The data is still there just cant not boot into windows now. Any tips on how to get my data off the HD before reformatting and starting again?
This would be best accomplished with a LiveCD. Something like BartPE or a distro of Linux.