I was having exactly the same problem as Pollux here.
I have a Windows 7 Home PC, with Shared folders that I access using a LGBD570 Wi-Fi Blu Ray player. When I had XP this worked perfectly, but when I bought the new Windows 7 PC, the shares disappeared.
After days of reading up, and fiddling with network settings, I was told to totally uninstall Windows Live Essentials, this worked as it did for Pollux.This was in October. No real issues since then, and I last used it on Thursday (12 Jan)
Then...yesterday (14 Jan), I settled down to watch a film. Nothing. Normally, restarting everything and hitting refresh server list a few times works. Still nothing. I checked no Windows Live Essentials things had crept in. No. I uninstalled every update since I last new it was working. Nothing. I checked the BD570 firmware. No change there. I looked for help in various online places, but there do not appear to be any changes. So now, I am totally stuck again, and my BD570 and PC are useless. Please not that the BD570 can see the PC - it shows the Windows Media Player Icon, but I need it to show the PC icon with the folders underneath.
NOW this is where it gets extra frustrating. I also have an HP Windows 7 Laptop. The BD570 see the shares on that perfectly. And the laptop has Live Essentials still on it.
I do not use media server software, as a) I find it slow and stuttery in playback, b) it is awkward about file types and c) it doesn't play subtitles, which cuts out about half my video library!
SOMEBODY PLEASE HELP!