Mystery crime files for Nintendo DS

Question

Mystery Case Files, Nintendo DS...I am NOVICE at this game...I have played two story mode games single player rookie mode...and solved both games...the problem is when I turn on the DS to play a new game it goes to the last sequenceof the game so I thought I had to redo the last sequence and did so in finishing the game..it stated I solve that particular file and ended with showing the credits of the people who invented the game..my problem now is that it won't let me play any new cases in either rookie or detective mode...I can play quick mode..but I want to solve more cases...I have covered the booklet from front to back for any useful info...and there is none to let me know what I need to do....can you help???