media player on network

Hi, I have a media player on my home network, which consists of 3 desktop pcs (1 xp home, 1 win 7 home p, and 1 win 8 pro) and 2 nas boxes. Nothing is wireless, all cabled. All pcs can talk to each other and the nas boxes, all have internet access. Problem is when I try to access pc files with my media player. It can access the nas boxes and the xp pc fine, but when i attempt the win 7 or...