|Have a look in Device Manager.|
Under "Network Adapters" is your wireless adapter listed there?
If it isn't, are there any "Unknown Devices" listed at all in Device Manager (question mark icon)?
If yes, then re-install the wireless driver which you can download from your laptop manufacturer's website.
If it's not listed anywhere in Device Manager, then the wireless adapter itself has probably failed.
You can overcome that by buying a USB wireless adapter, or if your laptop is still covered by manufacturer's warranty contact them to get it repaired.