The ibus is what controls the on/off, power is on the normal supply circuit, but it is ibus controlled.

At a guess id say the mk3 is failing. Id just replace it with a mk4, its a much better unit.

Also its running a really old version of OS, might be an idea to update it.

I have the cdkey image as well if you need it.

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Sept 03, M3, Silver Grey. Retro-fits: Modded Mk4 DVD Drive, OEM Bluetooth, VR Control, Rainbow Speaker Upgrade, Sony SOT Amp, HK Sub, CCFL, Intravee II, NightMode.