Retro video gaming cartridges as they get older can start to fail, either you can get garbled graphics on your screen or the game doesn't boot at all. The most common reason for this is that the contact traces on a game cartridge are no longer clean enough to connect to the pins in the cartridge slot in the console unit.
The "gunk" is basically dust and oxidisation built up over the years, natural "rusting" really, that forms a dirt barrier to prevent the game cartridge working as it used to do.
This is a very basic tutorial that costs nothing to fix the problem.
For the purpose of this demonstration, I have used a Nintendo SNES game cartridge however of course this tutorial will work for any other game cartridge as the principles are exactly the same.
Step 1: Open up game cartridge
First step of course is to open up the game cartridge, these are always held by screws, sometimes normal screws sometimes with special screws. That is why I chose a Nintendo cartridge for this demonstration as it uses non-standard screws.
Easy and cheap method is to get an old screwdriver and file the end into a groove so that it just fits over the recesses in the screw and will therefore turn it.
Then remove the screws.