untick the automatically restart box in control panel/system/advanced/start up and recovery/settings now you will get and error displayed instead of a restart.if the error points toward the graphics driver then
i would update windows to service pk1,if not already done so and get all the critical updates. click here
then click here select windows xp/graphic driver/radeon family and download the 3.6 driver and control panel,save them for later.
click control panel/add remove programs and click the ati control panel and uninstall it(do not restart)then click the ati( or 3 party) driver and remove it.restart windows.
install the new downloaded driver and restart.install the control panel and restart.