Originally posted by: Navid
I do not have an answer for you.
But, I know that one of the parameters XP monitors in order to decide if too much has changed or not is the volume ID of the partition XP is installed on. This parameter has 1 vote.
Amount of memory, CPU type, master optical drive, graphics card each have 1 vote also. There are some other parameters that each have 1 vote. MAC ID has 3 votes. The threshold is breached if you have less than 7 votes and reactivation will be required.
I do not know if the volume ID is changed automatically when you convert from FAT to NTFS!
Edit:
You can download and run xpinfo to see what components have changed since activation.
http://www.licenturion.com/xp/
If you have an image of your OS before the conversion, you can restore and run xpinfo on it to see if you were at the boundary and the volume ID change triggered it.