how to disable auto reboot on system failure

Win XP auto reboots repeatedly. The rebooting loop started after power
failure at power company and takes place every time I switch on the box.
Boot sequence gets as far as Post when it reboots. Can't access Windows
Advanced Options Menu to disable Auto reboot. Can't see any error messages
due to this. Is there a way of editing the registry in order to disable this
feature without logging on to windows? Recovery Console perhaps?


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