well the part about the screen dimming out and freezing before brightening up, is the gasp/scary part. Being an electronics tech, This is caused by a substantial short-term current surge. the system freeze really scares me because that meant that a voltage rail dipped below a certain point, and/or a glitch was induced in one of the power rails which sent the CPU into the weeds from a malformed instruction execution. Now the HDD doesnt spin, it could very well have been your +5v rail going bye bye, lost the MOSFET and the system drug down until a microfuse let go. Do you have a CDROM drive? Check to make sure it still ejects on its own. they both share the same +5v circuit. if the HDD dont spin, and the CDROM wont eject, then there you go.

its this result from a MOSFET or an IC chip deciding to go short during this time period.

Best thing to do is remove the HDD, and grab a meter to measure the rail voltage on the HDD connector of the powerbook. should be 5V. if its present, you lost the control IC for sure, or even bad PMU/PRAM settings. if its not, you lost the DC-DC converter circuit.