More info required please - What is the OS; have you Updated drivers or anything recently?
Possibly a simple visit to Device Manager would fix it.
First of all find the Wifi Network Adapter and uninstall it. Restart the laptop and let it reinstall the Adapter and see if this solves the issue. If not then select the Adapter properties and update the Driver.
If still no good, visit the Sony Website and download the latest driver for your OS.