Crazy box

We have a system at work that exhibits the following symptoms. You can see it fine from different subnets, but not from machines on the same subnet.

When you turn off the firewall it kills the mechanism that answers pings and advertises on the network. When the system uses DHCP, the DHCP server tells the rest of the network where the machine is. If you are on the same subnet, the machine is expected to advertise itself. Thus our problem.

This has something to do with services and the Windows Firewall problem. Is it fixed? I don't know. The system shows up sometimes and drops others. Someone else set this box up. That is not a problem, except I can't figure out what caused this issue. Normally, I don't mess with these settings and things seem to work fine. Now I'm wandering if it would be faster to just restage (start over and install the OS from scratch) rather than continuing to mess with it.