@gizmo350
Well, for starters, each computer in a simple PC LAN environment, known as a workgroup, must be a member of that workgroup to "see" each other. Crate a workgroup name something like "mylan". Join all computers to that workgroup and you should be good to go.
This is not required for networking to work. Ping works just fine regardless of workgroup.
Thus, this cannot be his problem.
@ChaosLord
Of course they are in the same workgroup!
How else would my LAN have worked all that Time?
Just fine.
The only thing that wouldn't work would be the samba connection. Ping, and every other network connection between the computers would still work.
Anyway, regarding the problem: One possibility is that the XP firewall has for some reason figured that your system must be blocked. Try temporarily disabling the firewall and see if you can ping then.