The OP wrote:
[[ So that is great. But now I'm afraid to turn it off and start it again when that time comes.
You guys have an idea what I can do before turning it off later? Pray and hope for the best? ]]
If you want to rid yourself of the anxiety, keep reading.
Your hard drive has become corrupted. It may be a software problem. These are fixable.
It might be a hardware problem. If something within the drive is failing, and becomes physically broken, the drive will be useless.
You need a backup, and YOU NEED IT NOW.
A BOOTABLE backup will ensure that if the internal hard drive again fails, you'll still have a way to boot the iMac and "get at" your stuff.
It won't cost much and it's EASY to do.
First, get one of these:
http://www.amazon.com/Optimized-Ina...732&sr=8-1&keywords=inateck+usb3+uasp+support
It costs about $19.
Then, you need to buy a 2.5" drive from the vendor of your choice. Check at amazon, newegg, etc. A good place to check for what drives are on sale is dealmac.com.
You can get either an SSD (solid state drive) or an HDD (spinning hard disk drive). The SSD costs more but is very fast. The HDD will have more capacity, but bootup time will be slower.
Since what you really need is a good backup that is large enough to backup your entire internal drive, a 1tb or 2tb 2.5" HDD might be a good choice.
Be sure you buy a 2.5" drive, and NOT a 3.5" drive !!
Once you have these two things, put the drive into the enclosure and snap the cover on. This will take you about 45 seconds.
Then, connect it to the Mac.
It's probably not yet initialized, so launch Disk Utility and initialize it for HFS+ with journaling enabled. Give the drive a recognizable name, such as "Backup drive", or whatever you wish.
Now, it's time to create a bootable backup.
You can use either CarbonCopyCloner or SuperDuper. I like CCC because it will also create a recovery partition on the backup drive.
CCC is FREE to download, and FREE to use for 30 days, from here:
http://www.bombich.com/download.html
Once you have it, launch it.
CCC is simple to use.
On the left is your "source" drive (your internal)
On the right will be your "target" drive (your backup)
Just set it this way and let CCC do it's thing (it will take a while for the first-time backup).
When done, TEST your backup like this:
- Shut down the computer -- ALL THE WAY OFF
- Press the power on button
- As soon as you hear the startup sound, hold down the Option key until the Startup Manager appears. This shows you all the bootable volumes available.
- Select your backup with the mouse or tab keys, then hit return
- The Mac should boot from the external backup drive -- it may take a little longer than booting from the internal drive
- When you get to the Finder, it should look exactly like the internal drive. This is what a "clone" is all about
- Do this, and you KNOW you have a bootable backup, if the computer ever fails to boot from the internal drive again, you can connect your backup and get running from that. Everything will "be there", just as it was on the internal drive.
This sounds like a lot, but it's EASY.
Work through it the first time, and it gets even easier and faster.
I can backup my "main files volume" in about 30 seconds.