Well if you understand how imaging works, you would know
When you have an image, it almost 100% for the same exact computer with the same mobo, vc, etc. I do this all the time and never needed to reactivate. I built 8 different images for 8 different computers and laptops. Now there are universal images that can be used on ALMOST every different type of computer but this requires a lot of work. I think Inaris uses this system. I just make a new image when we get new laptops/computers. And no it doesnt take months, thats another topic
As for his problem, a system disk error could me hard drive does not have bootable files on it, bad or not connected properly, or a couple other things. You said you have 3 XP installs to choose from, looks like you have 2 extra install that either didnt completely install or are invalid or are valid installs. You really didnt reinstall anything. You just made another partition on the same hard drive more than likely. If you can get into your XP, check the event viewer for any issues it reports. You may have a bad hard drive or something else. What you are doing wont work 99% of the time anyways unless both of your systems are exaclty the same.