Windows 7: Can't access my W7 computers from others on the network

Hi. I have four computers on a network. 192.168.1.100, 101, 102, 103. 100 is Windows 7. All four can connect to the Internet. The last three can see each other, but none of those can see 100. If I am on any of the last three, and go start > run > \\192.168.1.100, I get a message saying that the computer can not be accessed. It used to work, but no longer.

If I go to the Windows 7 N&S Center, I see that it belongs to Network/Home Network. The second two computers are Vista; if I go to the N&S Center there, I see that it belongs to Network5/Private Network. I assume this is the problem?

In Windows 7, I tried turning on Network Dicsovery, doesn't work. I tried leaving the homegroup to re-establish the computer on Network5, but I wasn't allowed to.

Any ideas on what I should do here?

Thanks in advance.

If you can't leave the Homegroup it can usually be fixed by following the link below.
Homegroup Not Working

You should be aware that Homegroups is not really made to work with other Op systems besides Windows 7 and 8. You will want to the Windows 7 machine to be on a Home network in order to set up the Homegroup.

It is possible to down level share with other Op systems with a Homegroup set up but the set up fairly complicated, the link below allows you to download a .doc file that shows you how to set it up.
Download Windows 7 & HomeGroup: Downlevel Sharing from Official Microsoft Download Center

Other problems can usually be fixed by following the Homegroup trouble shooter.
Ultimate Troubleshooting Guide for Windows 7 HomeGroup Connection Issues

Thanks for the time here

So, I took a look at the first link, and that's what did it - thanks!

Good guess on my part. When you can't leave the Homegroup that one usually works.