The "negation = Genitive" rule cannot be extrapolated too far. It works only when the positive sentence used Accusative. Otherwise, the case just stays. (which kinda means that it works also when the positive sentence used Genitive :P)
Computer again, it was not accepted, I thought that was peculiar. Judging by what mine less than a year old doeas to me at times, I can undestand. In the middle of a lesson I lose my screen and go to log on mode and nothing will bring it back.