When a stop error occurs it can seem like the system is just rebooting its self. You might see a flash of blue just before the machine restarts itself. This is because Windows XP is set to automatically restart by default when a blue screen error occurs. Open your system properties, click the advanced tab and then the settings button under startup and recovery. Uncheck 'Automatically Restart' and OK all of the open windows. Next time a stop error is generated you should be able to see it now.
you can also control the screen that allows u to choose an OS to boot if u have more than 1, or turn it off if u formatted a hard drive and it is still annoying you.