The error code 12 indicates a dead battery on the main circuit board, called the "mpu" board. This is a common error on an older machine that has been sitting for a while unused. You will want to remove the mpu board to replace the battery, plus inspect it to see if the old battery has leaked and is causing any damage. (you've probably seen flashlights with old batteries that leaked, it is corrosive).
When you post a few photos we can id your machine and give more specific advice. Posting photos is easy, when you are entering a message here look just below the message box and you will see "Attachments and other options" written in green. Click it and a dropdown will appear that will let you choose a file to upload and it will be attached to your message post. After selecting the photo file click on "Post" at the bottom and your message and photos will be posted. There is a size limit to photo files, so if they are too large you may need to reduce the photo file size on your camera.
The reset key is typically a "2341" key, they are available lots of places, including from folks here on NLG, ebay and slot machine parts places.