wifi no hardware installed after yosemite install but Bluetooth works fine

Reset SMC. http://support.apple.com/kb/HT3964

Choose the method for:

"Resetting SMC on portables with a battery you should not remove on your own".

I've had a very similar issue with my mid 2010 iMac, which had been functioning perfectly prior to upgrading to Yosemite 10.10 from Mavericks. Now my system is showing "no wifi hardware installed" and the ethernet is not functioning as well, although the Bluetooth is working. I've reset the SMC and the PRAM, and tried the numerous other fixes being touted here and across the web, all with no success, and so I called Support, and they claim it is "coincidental" and a hardware issue only. The "no wifi hardware detected" problem is showing up in threads and comments on numerous sites, and I think Support may not realize the difference between "coincidental" and "unintentional."

I've tried nearly every solution on the Apple Communities to address this "no hardware installed" problem since the Mavericks (10.9.3 or so) upgrade. The only thing that consistently works on my mid-2009 Macbook Air is to run the Apple Hardware Test (the full test or at least part of the full test--never run the briefer test, as it just doesn't work for whatever reason). This test gets rid of the "no hardware installed" issue temporarily, but turning the Wi-Fi adapter back on (I usually delete the adapter altogether) causes the same problems all over again (after the predictable lock up). Even if I use the hardware test to get the "no hardware installed" problem to go away (and hence, reactivate the Mac App Store--updates, purchased software, etc.), there is no guarantee that this workaround fix will last for long. It could be gone the next time I restart the computer and we're back to the beginning again. It's pretty obvious that this is a software-hardware issue because the Apple Hardware Test always shows that all of my hardware works and the card itself appears to be working again (at least present and available) immediately after the test (that is, after the restart). Apple seriously needs to fix this "no hardware installed" problem for everyone. It has been a major headache and has reduced my enjoyment and productivity considerably. I switched to Apple to get rid of these PC like issues, not to go through them all over again!

Yosemite has completely wrecked wifi. It's just about enough to make me switch to windows.

I've really tried every trick possible to get my wifi to come back and nothing is working! I am a web designer and graphic artist. Apple is costing me tons of money! This really makes no sense! Apple should be ashamed of themselves! You ******* spend so much money on trying to cheat people out of their money that you don't spend your money wisely in fixing all the glitches and problem in your dumb *** software ! At the rate you guys are going windows are going to knock you ******** right off the map!