Internet connection sharing suddenly dead?

[Jeremy]

I connected two computers with Windows XP into a network using a cross-over cable, and turned on Internet connection sharing on the PC that is connected to Internet through a wireless connection. I tried using Internet from the other computer, and it still worked. I used the Network Connection Wizard on both computers, and it continued working. I shared some files and folders between PCs, and then when I tried to use Internet from the computer that connects to Internet through the LAN, it did not work. And no matter what I did next, disable, enable anything, do a system restore on both computers, etc., Internet would not work! What is the possible problem?
The Internet connection is a broadband connection that is always on, so running Internet Connection Setup does not do anything