Tried to network media player all night- please help!

I bought a Western Digital TV Live HD Media Player. I am trying to set it up in my bedroom to play movies and music from two different external hard drives. On my network I have a computer running Windows Vista, a laptop running Windows 7 and a Playstation 3. The external hard drives are hooked to my main computer. I have shared the hard drives (E and F) and they show up on my Playstation and Laptop. My main computer is hooked to the router wired, while the laptop and media player are both wireless. I am using a D-Link router, if that helps. I also have a D-Link Range Booster USB Adapter. When I turn on the Media Player, and go into video or music and network settings or media server, it picks up my lapatop, not main computer. But then it says unable to find and media. If the laptop is off, it doesn’t pick up anything. I am not very computer literate and do not know a lot of the shorthand. I have been trying to figure this out all evening and I am very frustrated. I have tried reading different messages, but either they refer to Windows 7 or I just don’t understand. If you have any advice to give, I would really appreciate it. If you need any more info, please let me know.