1. Remove the ribbon cassette stopper and make sure the ribbon is wound firmly. 
  2. Insert the ribbon cassette as illustrated below, taking care not to catch the ribbon while sliding under the thermal head. 
  3. Close the printer lid.

The printer cannot detect the ribbon if the ribbon cassette or the ribbon itself is loose. When inserting the ribbon cassette, ensure the ribbon is wound firmly, and push the cassette until it touches its mount