There is a bit of your Apple computer that is called the System Management Controller (SMC), and it controls some hardware functions so that the otherwise busy main processor can be left to work on more important stuff. This piece of hardware sometimes malfunctions and your Mac will start to behave very strangely. Such as when the laptop’s fan goes on at full speed even if it’s properly ventilated. Or the MagSafe light goes out and doesn’t come on again even if your Mac needs charging.
There’s a whole bunch of quick diagnosis things you can do to understand whether you should think that the SMC isn’t working well. Click and read this Apple Support page to read all about these and about how to easily reset the SMC to get the whole system to work peacefully again.
I did it on my Macbook Air and it works. Read the support page before proceeding further.
Many seem to have problems getting to share their 3G internet connection over bluetooth between their iPhone and their Mac. It’s called Tethering. And if you look up this issue, many posts will just tell you to forget it because your carrier probably doesn’t allow it.
Persistence brought me to a solution. Macbook was telling me the pairing was successful. iPhone was telling me Tethering was ON, but that my Macbook had been discovered and “Not Connected”. The solution lies with fixing the Bluetooth PAN settings on the Macbook. But first remove all links that the iPhone and Macbook created between them during previous pairing attempts.
Here’s the blog post from @Peaz2.0 that tells you how to reconfigure Bluetooth PAN. When you’ve done it you can tether your iPhone 4’s internet connection with your Macbook. You will know that it’s working because a blue bar will appear on your iPhone just like the one below.