The NIC, or network interface card, provides a link between a computer on a network and the network's medium, usually a cable or a wireless signal. Though most newer computers have the NIC integrated with the motherboard, your laptop model may have a separate NIC, which can suffer damage through use. By using the Network Status indicator in your System Tray or "Device Manager" in "Control Panel," you can determine the functionality of your NIC by process of elimination.

Network Status

If your laptop shows no connection to a network, the problem can be due to factors other than the laptop's NIC. Ascertain that the problem doesn't lie elsewhere before attempting to replace your network card--you will save time, effort and money. According to a Microsoft article on troubleshooting network connections, your system tray in the bottom-right corner of your screen will display a "Network Status" icon if you have a NIC connected. This icon can show several statuses: "Connected," which indicates a problem with your router; "Limited Connectivity," which indicates improper configuration settings; "Unplugged," which refers to network cables; "Disabled," for manual disabling of the network connection; and "Not Connected," which refers to an inactive wireless connection.

Device Manager

If no "Network Status" icon appears in your system tray, it can indicate a malfunctioning NIC. You can use another utility to determine where your problem lies: "Device Manager." Click "Start," then "Control Panel." Choose "Device Manager" and open the subfolder "Network Adapters." After you find your NIC, right-click and choose "Properties." In the bottom of the window, a message will appear to indicate your NIC's performance. You may need to update the driver software, which you can do by right-clicking the NIC in "Device Manager" and selecting "Update Driver Software." Always create a "System Restore" point prior to updating drivers. If your network will not connect after you update your driver to the most current version and troubleshoot all other issues, you can safely assume you need to replace your laptop network card.

Source:

Microsoft.com: Windows XP - Troubleshooting Network Connection Problems