Windows 7: Network mapping issues

I recently discovered that for some unknown reason, the network map in our office is displaying differently than it did a few months ago. All that's changed is that I've added 2 new computers to the network. The network consists of 25 computers, a mix of 7pro, 7home, vista home, xp pro, xp home and one windows home server. Before this happened I had all the computers seeing each other by checking and changing all the following(if needed):
-Network discovery
-Proper workgroup
-Node type
-Send LM & NTLM – use NTLMv2

The current state is that there seems to be no pattern to which computers show up in the map and which ones don't other than that the xp comptuers see each other and a couple of the 7 computers and the 7 computers can hardly see anything.

What is strange is that if i type in the computer name whose share i want to access. I have attached a picture of what the network map looks like. Before I could see all computers on this map and in the root network folder (i.e. when you open explorer and just select network from the file tree).



Any help appreciated, thanks!