When i upgraded my pc with an Athlon XP 1800 and a motherboard with an modem onboard i sure installed Windows XP Pro . Then the install finished and restarts the pc ( normally ) . And when entered again in windows and i've started to set up my not onboard modem windows detected both and started to restart my pc without any explication and did not let me to choose the account and this thing happended since i installed again XP . I want to specify that the onboard modem was disable from BIOS . Some friends told me that this is a bug from XP and no patches available , after some weeks i installed again and worked . I want to find more information about this strange thing . Thank's to all !