Control Panel> Administrative Tools>event viewer, sort them the events there by error type, and check for any critical errors and read the message.
If there are no obvious problems there, check that you have the latest drivers for your raeon x1900, I believe 8.5 drivers were released a few days ago.
So this is only happening now when you try rendering animations?
What version of Max are you using, and what operating system?
It could be some issues with your CPU voltage, but i'll need your answers for the above first.