1. Are you running the latest version (10)? As of version 10, all of your hard drives should show up in the media pool. The top left of the media pool shows the folder structures of your hard drive. By drilling down these folders (by clicking on them in the top left pane) you should be able see the contents of them in the right column next to it. Davinci will only show the contents of media it can pull in.
When you click on a folder that you know contains media and you can't see the media in the right pane, the most logical explanation is that Davinci doesn't recognize the media. Maybe your file extension is wrong?
2. The free (Lite) version in V 10 is almost identical to the paid version. There are some differences like the supported timeline resolutions, but if you're just working in HD, you'll be fine with the free version. Maybe try it out first before diving into the paid one, to see if it's for you.
Whatever stage you are with your Post Production skill set, having Davinci under your belt can only be an asset. It's an incredibly powerful program!
Good luck,
Marcus H Smith