PC leds just flicker

Hello,

I am in desperate need of ideas here.
I am computer savvy but this phenomenon I have never encountered ever before.
My HTPC apparently has crashed in the middle of the night.
This morning trying to open it I found out it was not responding through RDP, no ping too.
So I decided to go see downstairs in my basement. It was lit but was emitting an intermittent led lights, the lights came from all the leds inside the case (fans, motherboard, whatever). The rythm was perfect (90bpm).
So i decided to plug it off the wall and wait. Plugged it in again but the same thing happened.
No signal comes out. No beep from the motherboard. Nothing appears on screen. All is lit, fans turns, leds blink at 90bpm. That's it.

How do you think i should proceed?

Always good to think in team.
So you suggest to just open it flat, disconnect pieces of hardware and try them back on one by one and see if I could get the motherboard to wake back up? Right?

It looks bad. Really bad.
I removed all my connections from the MB which are:
- nvidia 8600gts graphic card
- asus xonar hdav 1.3 sound card
- 1 seagate HD
- Thermaltake Bach case (iMon board included)
- 2 X 1Gb RAM Kingston

The only things left connected were the CPU and its Thermaltake Ruby Orb fan.
Even this way whenever I turned it on I could see and hear (from the fan) as if the current being fed to the motherboard was cut and back on at a very high speed of 90times/minute (measured).
That's what was causing the flicker of the led on the fan, but also on the leds on the motherboard.
And still no peep from the MB.
I have never seen something like it.
I think it is the MB.
Could it be a faulty CPU? Could this cause this effect?
Could it be the power supply? I mean everything is lit.
Any idea how to close on the problem?
I obviously cannot go and buy a new MB to eventually find out it is something else.

Thanks

Guys, thank you for your help. Against all odds it was the MoBo.
It just went dead. totally.
First time I saw that.