Chosen Solution

Hi there, Check to see that the connectors of the game cartridges and slot are clear of rust/dust and any other non-nintendo nastiness. If it appears all fine then I would suggest testing multiple games. If its only a select few games that aren’t working follow this guide to clean them out. Disassembling Nintendo 64 Cartridge When mine doesn’t work the first time flicking the console on and off a few times generally fixes the issue. Also check that the AV connectors aren’t dirty or grimy. If so give them a clean. You can also find replacement AV cables on Ebay, it might be worth trying another one. Another issue I’ve come across, if you’re using a newer TV you may have to change your TV picture settings from standard to game or dynamic. Lastly, make sure its plugged in correctly and the TV is on the correct channel/input. Its simple but it is surprisingly common. I hope these help.