Hi,
For a full list of steps to try, see the Wired and Wireless Tutorial on this page:
http://windows.microsoft.com/en-US/windows/help/wired-and-wireless-network-connection-problems-in-windows
After reading through the thread, if you feel any confusion regarding Wireless Networking technologies and configurations using Windows 7 , try using the basic troubleshooting steps given below.
1. First try and power off your modem, router and desktop/laptop. Then power on the modem, then the router, and then finally the desktop/laptop. Please do this in that order, allowing 60 seconds in between each device to enable the device to be fully booted and able to accept connections.
2. Update the drivers for your wireless network adapter via Windows Update, or by using the website for either the company you bought your PC/Laptop from or the manufacturer of your networking device.
3. Ensure that your router is set to broadcast it's network name (SSID), ensure that you are connecting to the correct wireless network (SSID) and that you are using the correct WEP/WPA passkey on both devices.
a. Please use "Windows Connect Now" or "Wi-Fi Protected Setup" if available on your wireless router to ensure that the connection is setup correctly.
4. If you are trying to use WPA or WPA2, please ensure that both your network adapter and wireless router support this protocol. If you are having issues detecting your wireless network when using WPA or WPA2, try configuring your router to use WEP instead and see if you can connect.
a. Please note that the change between WEP/WPA/WPA2 will need to be made on both your computer and wireless router.
b. If you are only able to connect using WEP, then your networking hardware may need a firmware upgrade. If you are not comfortable doing this yourself, please call your hardware/router manufacturer for help in doing this.
5. If you are having a problem with your wireless connection after resuming from hibernate or sleep, or are having intermittent connectivity issues, try to adjust your Power Management profile to change your Wireless Adapter Settings to Maximum Performance.
a. To do this click "Change Plan Settings" next to your Power Profile, and choose "Wireless Adapter Settings" and set it to Maximum Performance. You should do this with all of your power profiles. Additional guidance is available here: http://windows.microsoft.com/en-us/windows7/products/features/power-management
6. Call the support line for your router manufacturer. It is likely that neither Windows nor the router are having problems, it is simply an issue of getting the configuration settings on both set up to work correctly together. The router manufacturer will be the best resource to know how to configure their device. Most of the contact numbers are listed here: http://support.microsoft.com/gp/vendors/en-us