That is the symptom I have - no BSOD, no hardware messages, no stop codes, and no warning - straight into loss of display, a report from my LCD monitor of 'no signal', then the BIOS boot sequence.
It seems to be associated with user-initiated program activity rather than programs at rest, but that is the only clue I have. It can be any program at any time, mostly early in.
It started about 2-3 months after I upgraded to XP Pro SP2 from Win98 (end of 2006). The early occurrences were spaced about 3 weeks apart, but the interval has gradually shrunk until today it is almost guaranteed daily.
I cannot associate the start of the problem with any specific hardware or software change on my system.
Windows Memory Diagnostic found no problems. But something, somewhere is issuing an NMI that bypasses the OS messaging mechanisms.
I am considering trying an XP in-place repair, but before risking disturbing a loaded work-horse machine, I thought I should try to see if anybody in this impressive forum has advice, suggestions, prayers, or magic spells that might throw some light on the issue.