Hello,
I just gave away a janome 300E to my grand daughter. Do you have the card reader that came with the machine?? You must slide the card into the card reader, the put the reader device into the slot until it clicks. No need to be rough with it either, it should easily slide into the machine. YOu then push the button on the machine that shows the card reader and your designs should show up, keep in mind this may take a few minutes for it to load the designs so be patient please 
Hope this helps you out a little bit 
Judy 
Help me to start each day with a new attitude and plenty of gratitude!