Reboot in safe mode, and try to install the arcadeVGA drivers. Windows could be trying to use the stock ATI drivers.
Additionally, reboots and unexpected shutdowns shortly after startup can also be a sign that your computer is infected with the Sasser worm, especially if you did not install the KB835732 security patch yet. You can get this patch from WindowsUpdate.microsoft.com, and the removal Tool from Microsoft.com, Symantec.com, and McAfee.com.