Hawkeye22 is correct with the issue possibly being a bad card or the driver needing to be reinstalled.
There are some other things you can try though. In some instances, the network configuration that you receive from your Internet service provider might be incorrect or need updating. To fix this, reset your modem to reestablish the connection. One more thing is to make sure the card is seated properly in its slot. Another resource is this Microsoft support article that can help troubleshoot further if necessary.
One more thing worth mentioning is the upcoming Windows XP End of Support date, which is April 8, 2014. It is strongly recommended that users make the move to a modern operating system such as Windows 7 or Windows 8 by then. To find out more about what end of support means and what you can do to prepare you might be interested in this Springboard Blog post by Stephen Rose.