answer:I bought a used N64 a while ago and got some of those same issues as well — sometimes nothing came up on the TV, but not always. In my case, it seemed to be the game cartridges; some of them worked every time, others worked whenever they felt like it, and one has never ever worked (Donkey Kong 64). I tried everything and the only thing that seemed to help was dipping a q-tip in some glass cleaner (Windex) and rubbing that back and forth vigorously on both sides of the cartridges’ contacts — I remember that making a noticeable difference for at least one of my games. Ultimately, I just gave up on it because it was such a pain to get anything running.