Does your laptop have a Fn key? You probably need to press that and one of the keys on the very top row. My laptop actually has a separate key (larger keyboard) for the Prnt Scrn button, but in an older laptop I had, it was accessed using the Fn key.
The exact location might vary, if its not in the 5 rightmost keys on the very top row, then look around on the keyboard.
Edit: For the .ppm, I've seen them show up in the directory that you put TPT in.