Mysterious Problem

[caddolake]

POTC works on only one of my four computers. All are Dell. The one that it works on is the oldest. All are hardwired with Cat 5e cable to a home network. None are wireless. The one that works is not the main computer for the home network.

Here are the specs for the one we CAN play on.

Dell Dimension 8300
Windows XP SP2
Processor - 3ghz Intel Pentium 4
Graphics Card - Radeon 9800 128mb
Ram - 1 gig
Hard drive - 150gig (138gig free)
All Drivers are up to date per Driver Detective

Here is the specs for the three that Crash as soon as you click on "Play".

Dell Dimension 9100
Window XP Sp2
Processor - 3.5ghz Intel Pentium 4
Graphics Card - Nvidia 6800 256mb
Ram 1 to 1.5 gig
Hard drives - All over 150 with at least 125gig free
All Drivers are up to date per Driver Detective.

I have changed Modems and Routers, but nothing helps. The answer has to be simple but POTC support hasn't got a clue. All they keep saying is it has to be my ISP. I told them if one runs, they all should run. I even by-passed the router and that didn't work either.
HELP!!!!!
Sorry for the double post. Wasn't sure where to put this.