Hi all,
I apologize in advance for the long post, this was a problem I had for quite some time and managing to solve it without even understanding how (I am a newbie about electronics) is a kind of miracle, so I wanted to share it to see if someone can explain what exactly happened, I will go by chronological steps:
1 - I ordered on ebay a chinese oem motherboard for a workstation, which worked fine but it broke because of a short (my bad, something conductive was on the back of the board) in one of the inductors of the cpu power phases
2 - I got a replacement on warranty (lucky!), but when I installed everything I realized that probably also the cpu got fxxxed because the system was not posting (but at this point it was at least powering up, this fact is important)
3 - I ordered a new cpu, but when I installed everything the new board was not powering up anymore, completely dead, at this point I started to check online if it was possible to understand what was wrong with a simple multimeter.
4 - after quite a lot of googling, I gathered up some information on the very basics of how power is delivered to a motherboard once the power button is pressed.
5 - I checked the voltage on the power button pins (3.3v), on the super IO chip (3.3v in and out), on the 10th pin of pcie slots (3.3v), on the green and purple wire of the 24pin psu connector (4.5v), and for continuity between the ground on the motherboard and the 24pin connector, and everything looked fine.
6 - having lost any hope, I remembered that an Indian guy in one of the videos I watched was pointing to the 32khz crystal, but I had no idea on how to check it (maybe with an oscillator?), so I decided to replace it cannibalizing an old motherboard, and TADÀ, the board booted fine! I tried also the first cpu, but it looks like that one is not working

Now, my questions are: How did the first cpu broke? and how did the crystal in a new motherboard broke, maybe because of the dead cpu I tested on it first? also, a curious thing that happened when a I was trying the replaced board with the dead cpu (step 2), the 2 atx power supplies I used have "lost" the functionality to start when shorting the green wire with the ground wire on the 24pin connector (like when you want to use them as a bench power supply) but they still work when I use them normally in a motherboard, anyone have some idea of how is this possible?

 

how did the crystal in a new motherboard broke

It may have been faulty when installed in the factory, or there may have been a poor solder joint.

 

the board is now dead again, I will try to replace the crystal it when I find a new one, is it possible that a bad psu might cause the 32khz crystal to malfunction? other what might cause this problem?

 

Never buy Chinese parts from outside your geographical reach. Doing so will make warranty impossible.
The financial advantage is not high enough to take the risk.
Your better of buying local.

Picbuster

 

I know that buying an unknown chinese brand motherboard is not the most reliable solution, but this was the only m-atx motherboard with an intel 2011 socket I managed to find, and I bought it from an online european store which had no problem in replacing it when I sent them back the faulty one (which failed because I caused a short on the back, btw), and so far the board had been working better than I expected.
Now the issue with this new one looks like something wrong between the startup chip and the 32khz crystal used by the real time clock in the bios, and since the crystal fails when the board is not connected to the psu, it should be something between the cmos battery and the crystal that goes wrong.
Now forgive me for the very newbie question, but if I check for continuity the very very tiny smd capacitors and resistors on the board, shouldn't they all give me a connection if they are working? Because I found a resistor next to the crystal with the number 165 that doesn't pass the continuity test

 

How are you doing your 'continuity test'? With a bog-standard DMM, that's normally for low impedance measurements, so capacitors and non-low value resistors would show as open circuits. 165 would suggest a 1.6Megohm resistor.

 

right, but then when measuring the resistance I should get some measurement (I set it on 2000Kohm scale), instead I get nothing, whereas when I measure a closer resistor with 163 I get some result (I guess around 1600Kohm, but I don't remember now)