Is it a Core 2 Extreme X6800?
No, it is a core 2 extreme 2,66 ghz 8mb and the mainboard is msi p31 c33 DDR3. Actually I don't know the exact model of the cpu,but all i know is that it ran ok on 4 cores lately and that the problem was not caused neither from the bios nor from the system because I updated the bios and reset the system with the same results. I think I will have to take the case to a specialist because this is really an odd thing.
Thank you anyway.