It shouldn't be. It was bought in a regular store, and worked at 2.6 MHz with x13 before. I will go look at that software you recommended, and get back later with results..
Oh my mistake. The old one was series 2xxx, released same time as the MoBo (~2006). Since it's too old, I had to replace it with newer one - E3400 (released in 2010)
Intel BIOS does not support it. Latest BIOS version is from 2008.
So it seems it can't work on this MB. Intel motherboard, Intel CPU, both 775 but not compatible. Lame.
Thanx anyway for help.