You may have had an experience with your computer that caused it to now reboot everytime the AGP400.sys driver is accessed either in normal Windows startup or in safe-mode.

As I searched all over the internet, nothing concrete in the forums surfaced, but I did find this article from Microsoft. It helped me to resolve my issue, I thought I would post it so other found a solution to this problem. Good luck, here's the link.

http://support.microsoft.com/kb/324764

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