Year 3, Pursuing Peter Pettigrew

I'm on the iPhone, and I'm at the first part. I can't get the first key after the dementors. I transfigured the statue, but it went into a platform, and it's to jump on to the wrong bookshelf, the one without the key. I tried shooting the key from the other shelf,I tried jumping onto the other shelf, I tried talking to all the paintings. What do I do?

U jump on to the table from the (non key) book shelf then jump on to the other bookshwlf

I can't get past the prefect to get to the chest after getting the 1st key on top of the bookshelf. I can't use my invisibility cloak either. Can someone please help?!