networking 2 computers

I have 2 computers that need to share a cable internet connection. The both are running Windows XP Pro with SP2 and although the sharing is enabled on both computers, one will not surf the net or connect to any messengers (Yahoo or MSN). I click the properties of the connection and I see that it shows packets sent and received, but can’t surf the net or connect messengers. How do I fix this? The master computer is using a USB connection from the cable modem to the computer, then there is a crossover cable that connects both computers.