Hi,

First of all try this:

1. Use Windows "Troubleshoot problem" (right mouse click on the network icon on the task bar near to the clock).
2. Open "Device manager" and find your Wi-Fi card (something like Atheros, Realtek, Broadcom, etc.). Press the right mouse key on it an uninstall the driver.
3. Now restart the PC and Windows will reinstall the WLan driver. This will reset your Wi-Fi driver.
4. If this not fix your problem then you need to open the laptop and reconnect the wlan card.
5. The final step is Wi-Fi card replacement.