1. Disconnect AC adapter. Remove the battery.
2. Press and hold the power button for few second. (15 secs would be more than enough).
3. Restart your notebook.
If the problem persist try the following:
1. Re-install your wireless drivers.
2. Clean your wireless card (similar process to clean RAM)
-open the back of the computer and take out the wireless card.
-Clean the gold part(discharge) using eraser.
It could be expansive to replace the wireless card if turn out the card is faulty. So you can get a USB wireless stick which cost about $6.00 .