i don't know what happened, but the Nvidia card is not seen by the system, at all!
i tried a new driver from both Nvidia and Dell, the install could not detect the hardware
it still has "optimus" setting in the bios, enabled; i tried turning that off and there was only black screen when i rebooted! i fixed that part by removing the CMOS battery for a minute.
any help here? i also tried an older BIOS, because i already have A17 the latest.
so now i have only the intel HD4000 graphics from the cpu.