Why can't I open my ps2 ISO files when I try to mount them?

I downloaded Ratchet and Clank : Deadlock for my PS2 emulator, PCSX2, and I'm having trouble mounting it. The emulator works - I've tested it. I've tried using both MagicISO and DaemonTools Lite. When I put the folder for my ISOs on my Desktop or Doents, I can open the folder, but the files aren't there. The emulator just goes to the ps2 screen that says "Please insert a Playstation or Playstation2 format disk". Can I get some directions on how to correctly mount these? Thanks.