Network Refuse To Communicate

Hi all,
There is this network of six computers i’m working on. The organisation got an Internet Connection that was shared among the network computers. At first the setup worked for about a week. Then all of a sudden the access became epileptic. Only about 2 0r 3 computers could connect. The server is running winXP. And I’m using Internet Connection Sharing. On trying to troubleshoot the HUB the entire connection came to a halt. No computer could ping another. I’ve checked the HUB on another network it worked fine. I’ve checked the cable with a LAN tester they all fine. But I still cannot ping any computer on the Network.

Tata
NetAdmin
CIT BUK