I had a similar problem, and just figured it out. My WDTV live worked perfectly for about 6 months, then all of a sudden I could not access my shares. I am running Windows 7. I found the problem to be that my computer browser service was set to manual. This service maintains the list of devices in the network. After setting this service to automatic and then rebooting my computer, everything is good again.
1) Hit the windows key on your keyboard, then type “services” in the run box.
2) Click on “services” from the list.
3) Check to see if "computer browser has been started, and what mode it is in. If it is in manual, change it to automatic, and reboot your computer.