I have problems with a Sonoace which does not turn on. I am not sure whether it is a software problem or a power supply problem.

I can switch on and then the fan is turning and the hard drive starts spinning (but no 'reading sounds') CD drive I can open.
But the monitor stays dark (not a sign of booting). An external monitor on video out also stays black.
Keyboard buttons are all dark except the gain knob and the update button. These two are illuminated. All bottons are not functioning.

When I take off the PSA I can see the LEDs of the power supply unit. They are all on, except HV (5V, 12V, 97V are OK,the yellow LEDs (protection fuctions) are off).

My questions now would be:

1. Is this correct or should HV be present? (PSA is still off and system not yet booted.)

2. Or can it be a software problem? Does the machine usually show the boot process on the monitor? If so, does it mean the BIOS does not work? Can I enter the BIOS somehow?

I would be grateful for any tips.

Best regards