Well, if you haven't changed the setting it will automatically start playing the disc inside when you do fire it up. They added an option to have the disc autoplay turned off at startup in one of the recent system updates. If you are quick, however, you can quit the disc to make it stop playing and try to eject it. If the coin is rolling around loose on top it shouldn't jam anything up.
You will have to turn it on to be able to transfer anything from the hard drive. I do advise caution if you do decide to open it up yourself- we have seen a number of cases of people going into their system to try to "fix something" and have disconnected a cable that is vital to the whole system.