I made another exploration. When I set "Init Display First" from "AGP" to "PCI Slot" in bios, the problem reverts - everything works fine with Ati, but when I try to start X on Nvidia, the computer freezes.
I made another exploration. When I set "Init Display First" from "AGP" to "PCI Slot" in bios, the problem reverts - everything works fine with Ati, but when I try to start X on Nvidia, the computer freezes.