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You may find the steps in this article helpful with diagnosing the Wi-Fi connection issues you're seeing:
Wi-Fi: How to troubleshoot Wi-Fi connectivity
All the best,
I have exactly the same issue Nik, first my MBP was dropping connection and then coming back on a restart. Now it is non existent and when you try an turn wifi on it says "Wifi: No Hardware Installed." Bluetooth has also ceased working. I've attempted a restart, an SMC reset, a PRAM reset, none of which have any effect.
Anyone who can shed any light on how to fix this, you will be forever in my debt.
Macbook is 13" early 2011, on 10.9.1 Mavericks.
Result. My wifi is back working again.
After a number of evenings trawling through the support pages, I found a youtube clip from a chap taking his macbook apart and locating the airport adaptor and connecting cables.
The cable in question is located in the black plastic bar below the display and is a pain to get to. Apprently the most common cause of this issue is the cable becoming dislodged through an impromptu knock. I can see how this happened to me by travelling on the London Underground everyday with my mac in my shoulder bag.
Anyway, having seen the video, I bottled it and went to the genius bar obviously having seen the clip. I had a worst case scenario quote of £95.00, but a quote for a replacement cable and reseal being much less. I'm quite savvy but my mac is sacred and i'd rather the pros did it. Turned out to be £37.00 and my mac came back fixed and clean.... £37.00 for piece of mind is well worth it.
Here's the youtube clip but please don't take unnecessary risks. http://www.youtube.com/watch?v=UsSIUs7jzQc
Best of luck all.