It sounds like you are trying to re-install XP.
The NTDETECT error might indicate a hard drive problem.
I always start with the basics. First I run a DOS memory diagnostic. You can search for "memtest86" or "microsoft memory diagnostic".
Then I run a DOS hard drive diagnostic. Every hard drive manufacturer has one, and you don't necessarily have to use the one from the manufacturer of your hard drive.
There are more ways to help find the problem. Trying to run a "live" Linux or the "Ultimate Boot CD for Windows" can be informative.