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Yes that worked perfectly. &nbsp;<br />
I had to switch off wifi, and the first time I did it, I did a re-boot before re-installing os, and that made it go back to how it was.<br />
I had to erase the old partition as journaled, but all installed ok.<br />
<br />
Now just updating to Sierra.<br />
<br />
thanks<br />
<br />
Terry
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Yes that worked perfectly.  
I had to switch off wifi, and the first time I did it, I did a re-boot before re-installing os, and that made it go back to how it was.
I had to erase the old partition as journaled, but all installed ok.

Now just updating to Sierra.

thanks

Terry

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<div class="content wysiwyg-content">
I tried to reset to Factory default a MacBook Air, but have ended up with OS X Base system set for the whole of disk. &nbsp;<br />
Not sure what I did, I thought I was installing os but added OS X base system instead.<br />
But now when I try and install OS X it says my disk is locked.<br />
And in disk utility I can't reduce or unmount.<br />
<br />
I am new to this, please can you help.<br />
<br />
Thanks Terry<br />
<a href="https://filedb.experts-exchange.com/incoming/2017/02_w05/1142677/Screen-Shot-2017-02-03-at-22.30.21.png" target="_blank" class="file-inline" title="Screen shot (476 KB)"><svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 512 512"><path d="M67.508 468.467c-58.005-58.013-58.016-151.92 0-209.943l225.011-225.04c44.643-44.645 117.279-44.645 161.92 0 44.743 44.749 44.753 117.186 0 161.944l-189.465 189.49c-31.41 31.413-82.518 31.412-113.926.001-31.479-31.482-31.49-82.453 0-113.944L311.51 110.491c4.687-4.687 12.286-4.687 16.972 0l16.967 16.971c4.685 4.686 4.685 12.283 0 16.969L184.983 304.917c-12.724 12.724-12.73 33.328 0 46.058 12.696 12.697 33.356 12.699 46.054-.001l189.465-189.489c25.987-25.989 25.994-68.06.001-94.056-25.931-25.934-68.119-25.932-94.049 0l-225.01 225.039c-39.249 39.252-39.258 102.795-.001 142.057 39.285 39.29 102.885 39.287 142.162-.028A739446.174 739446.174 0 0 1 439.497 238.49c4.686-4.687 12.282-4.684 16.969.004l16.967 16.971c4.685 4.686 4.689 12.279.004 16.965a755654.128 755654.128 0 0 0-195.881 195.996c-58.034 58.092-152.004 58.093-210.048.041z"/></svg>Screen-Shot-2017-02-03-at-22.30.21.png</a>
</div>
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Screen-Shot-2017-02-03-at-22.30.21.png

I tried to reset to Factory default a MacBook Air, but have ended up with OS X Base system set for the whole of disk.  
Not sure what I did, I thought I was installing os but added OS X base system instead.
But now when I try and install OS X it says my disk is locked.
And in disk utility I can't reduce or unmount.

I am new to this, please can you help.

Thanks Terry

Reset MacBook Air to factory settings

Mac OS X is the desktop operating system from Apple Inc., found on Macintosh computers. OS X consists of a Mach/BSD-based kernel, operating system interfaces primarily based on FreeBSD and additional frameworks (written in C, C++ and Objective-C providing user interface and application-level services.