Performed the re-seating but it seems that even on the slightest move the upper cpu gets dislocated (even though it has no visible signs of dismounting it just doesn't get recognized). Next step is to determine with certainty whether this is a problem caused by the cpu slot on the logic board (hope not) or from the huge heatsink.

In the meantime, pampers, do you happen to have kept the water-cooling system or have a spare heatnink in case any of the aforementioned are needed?