Can you give us more information and/or image of the knob. We have gone over our laptop and can't find it. Is it near the volume? We can only find the light there. We have a L550.
I have a solution that i found on the net. I had the same problem except, my satellite was brand new, and even when i would use the function keys, nothing would work. So, first disconnect your laptop from power, remove the battery, and press the power up button while holding it down for atleast 30 seconds. i know it sounds weird, but that's what i thought at first, and it worked. Ofcourse while holding down the power button, nothing will come on as there is no power source. after you're done, put the battery back on and connect the laptop to power, then switch on the laptop, your wifi should be working. Although, you should always have the battery atleast half, or connect the laptop to power when using wifi. however, that's how i dealt with it. Hope it helps and works. post back if it does