I had this same problem with my Dell XPS. Chances are you computer has the same problem. If you haven't fixed it yet I have some problem solvers for you.
1. You're not running the latest drivers. (Easy installation)
2. It may not be your WLAN Card at all. It could be that your laptop is overheating and your computer responds to save your motherboard from overheating. Your card might just stop working because of this.
Where is your laptop located? On a desk or some sort of flat surface?
Do you have a fan running underneath it?