Or someone's standing on the cable :-) Yes, a bad spirit!!!
I resume. 1-The problem occured after I tried to share my Epson printer between my three PCs: Gentoo+XP (twice) and W7 2-The NIC is included in the motherboard (Asus P5K-E) 3-The cable from the dektop, where the problem exists, works fine on the laptop which is without problem, and the cable from the laptop doesn't work on the desktop. Therefore, I think, that's not a cable problem.