If you have Nintendo N64, Super Nintendo SNES, or any of the Gameboy games cartridges that do not work, clean the electrical contacts on them using an alcohol based cleaning material & cotton bud.  Leave to dry for a couple of minutes & hey presto, load up like new!!!  A heafty blow into the contact end of the cartridge & console also usually does the trick!!  Check out my own N64, SNES & Gameboy games at Retro Chakras!!!!