Change in routers breaks remote desktop to one computer (LAN)

Background: Little home network, 4 computers I regularly use. Main PC, Win7Pro64, connected by WiFi, other PCs, all Ethernet to the router, Win7Pro32, XPPro, Win2KServer. (I never can bring myself to get rid of a computer). Anyway, all working moderately well, Main PC can remote desktop to all the others, and see shared folders.

Then some problems: Due to some erratic speed (initially thought my internet speed, but trouble shooting hints at LAN), I was experimenting, and it seemed that my old Netgear router was acting erratically. Continuing to experiment, I replaced the router with a somewhat newer D-Link router (One I had bought ~18 months ago, but didnt like some features, and it has been on the shelf.)

The D-Link seemed to make an improvement in speed, but the problem was very intermittent, so, I am still playing with it. But, here is my problem. The Win7Pro32 computer is no longer available by remote desktop. The other two are fine. and all three show their shared folders. Just no remote desktop on the Win7 computer. I have swapped the routers until I have about worn out the cable connectors, and the D-link just does not allow remote desktop between the Win7 computers.

This is likely something obvious to someone who understands networking, and I dont. I just keep changing settings, reconnecting and rebooting until it works. No suggestion rejected.

Fixed--Control Panel, Homegroup, Join Homegroup. Win7 PC thought it was on a public network. I assume that sometime in the past, I had trained it to recognize one router as "Home Network", where the other router had not received such blessing. Surprised that it would share files anyway, but thats apparently the story.