|Is the network interface on your computer set to "Get IP address automatically" (DHCP)?|
Are you connecting directly to the PC from the modem? If yes, and your modem isn't a combination modem/router/wireless AP I highly recommend you buy a SOHO Router and plug it in between the internet and your PC.
It matters not how straight the gate,
How charged with punishments the scroll,
I am the master of my fate;
I am the captain of my soul.