Sometimes an iPhone can get into an ill-configured state and become unusable. It may have happened thanks to, euphemistically, Cosmic Rays or an airport security system. Or it could have been due to some software you downloaded that failed miserably and borked the iPhone for good.  Now, you'd like to try a software restore, but it won't mount in iTunes. Here's a process that might fix that.

In some cases, connecting an iPhone, via USB2, to your Mac and iTunes produces no result at all. The iPhone won't mount, it won't display in the device list, and there's no apparent way to resuscitate it. Your breathing becomes labored.

Something similar happened to one of our editors recently who downloaded an app that so damaged his iPhone that he needed to do a complete restore.

The key is forcing the iPhone into recovery mode, as outlined in Apple knowledge base article # HT1808. Go read that, but here's a summary:

1. Disconnect the USB cable from the Phone. Have the other end plugged into your Mac with iTunes running. I'd suggest bypassing any dock you may have.
2. Power off the iPhone by holding the power button down until you see the red slider, then use the red slider to shut down. If that doesn't work, try holding the power button and the home button simultaneously until the iPhone powers down.
3. Next, and here's the key part, press and hold the home button while connecting the USB cable to the iPhone.
4. There should be some beeping by the Mac, and then you'll see a dialog box that says an iPhone in recovery mode has been detected. Click "OK"

The iPhone should now be recognized by iTunes. The next step, is to restore the iPhone software and firmware from a previous iPhone software file. These files end in .ipsw.

If you simply click the "Restore" button, iTunes will select the latest .ipsw file. However, if you have another, older file in mind, you should know that all these files are located in:

/Users/your_home_dir/Library/iTunes/iPhone Software Updates

Where "your_home_dir" means your actual account name, for example, "david" (without the quotes). To see a list of all the updates that have been downloaded, press and hold the OPTION (alt) key when you click on the Restore button. This will bring up a file open dialog that looks like this:

Hold Option key & click Restore button to get File Dialog

For most users this will suffice, but if you've legally unlocked your iPhone for personal use, you may have a different file that you wish to load. Use the File open dialog shown above to navigate to that file instead. The iPhone will go through a rather long process of reinstalling the software and firmware, and then restart. Patience is necessary here.

After the restore and restart is done, iTunes should then trigger a reload of your personal data from the latest backup.

Having an iPhone fail to boot up properly because the software is damaged and then fail to mount in iTunes can be a scary experience, but this process may help you restore the iPhone to its original Apple software and get you breathing normally again.