Blue screen trying to boot XP PRO

Hello, I have a PC that would not startup and the customer took the HD out and put it into another PC. When it did not boot she put the HD back into this PC and we changed out the power supply and now it startsup but when it is going thru the Windows screen, it starts back all over again and comes up with the screen showing START WINDOWS NORMALLY and then starts all over again and just keeps repeating the start process without ever completely booting up.