My XP Pro machine will no longer see my Time capsule.

Question

Just before Christmas, I switched from Embarq DSL to Cox Cable.
When I was with Embarq, I had a static IP address but now that I am no longer with Embarq, I no longer have a static IP address. I am mentioning this out of completeness and (as far as I know) for no other reason.
My set up is as follows:
Arris Cable modem (supplied by Cox Cable).
This goes into a Netgear GS105 switch.
My house has Cat6 cable wired into the wall and goes to the following four outlet:
1) My old office - this is where I have my Dell Dimension running Windows XP Professional
2) The closet - this is where I have a 1 Gb Time Capsule connected to a Belkin router which has 3 1 Tb external drives attached to it.
3) The media nook - I have noting attached to this (I did it ready for when I get my HD TV and a Blu-Ray player).
4) The bedroom - I have my iMac, running OS X 10.5.6
Before I switched to Cox Cable, everything worked perfectly:
My iMac could see my Dell and the Time Capsule AND the three external disc drives.
My Dell could see mu iMac and the three external disk drives (it could see the Time Capsule, but did not know how to access it, of course).
Everything could see and access everything else.
Then I switched to Cox Cable.
Now my Dell Dimension, running Windows XP Professional can see the outside world (Internet) but cannot see my iMac, Time Capsule or the three external hard drives.
My iMac CAN see my Time Capsule, three hard drives AND the outside world (Internet).
I would like everything to be able to access everything, just as it used to.
Cox cable have said "it's not our problem...we get Internet to your house and that's where our responsibility ends."
Nothing has been changed on any computer other than I made sure that all the IP addresses were assigned by the Cable modem and I no longer had the IP addresses hard coded into my PC.
Nothing else changed. I have switched off everything and unplugged everything.
The sequence that I power things up is:
1) Reboot the cable modem (it has an 8-hour battery backup built in, so just switching it off does nothing). I wait until it has powered up and all the lights are on as expected.
2) I power on the Netgear switch.
3) I connect the Ethernet cable from the cable modem to the switch and make sure all the lights on the switch light up as expected.
4) I connect the Ethernet cable to one of the computer (Time capsule or iMac or PC) and then switch on that computer. It will see the Internet.
5) I connect the Ethernet cable to the next computer (Time capsule or iMac or PC) and then switch on that computer. It will see the Internet.
6) I connect the Ethernet cable to the last computer (Time capsule or iMac or PC) and then switch on that computer. It will see the Internet.
The iMac will see the Time Capsule, the three hard drives and the Internet but not the PC.
The Time Capsule will see the network.
The PC will see the Internet but nothing else.
What is the secret here?
Nothing changed EXCEPT the cable modem and Cox Cable swear blind that it is NOTHING to do with them, yet it will all work if connected to an Embarq DSL modem, rather than a Cox Cable modem.

Answer 1

It's NOT a firewall issue. The FIRST thing that I do with any Windows installation is to disable the firewall. I have just checked and the firewall IS disabled on the OC.
Yes, I CAN ping my mac from my PC.