Halo, i have a Samsung IDCS 100 and suddenly the telephone screens only showing version number and nothing is working.

I believed that the PSU had failed and gave it and was repaired by a proffesional repairs store but the problem still exists.

I also gave to the same store all the boards and they found no problem.

Does anyone have any idea of what might be the problem and how to solve it or even at least find out only?

I even phoned to a professional installer and informed him that i repaired the psu and what are the symptoms and says it is the mainboard.

I believe it is not the mainboard.

Sounds like the psu or the processor.
If it's the processor you're going to have to find a2nd hand of as that system isn't made anymore, and hasn't been for 5+ years depending on your region.

nameless is right.First up the power supply then the main processor . 99.9 % of the time that is the problem