Q: iMac stuck

As long as you are in single user mode, go ahead and repair your HD. Here is a link with instructions:

http://www.everythingmacintosh.com/tech-notes/repair-your-hard-disk-in-single-us er-mode/

Do that and then reboot and report back.

It is not "DOS" that you are seeing, but the command line prompt. It is actually how computers work, and what you see is the Single User Mode with a typical prompt. (meaning it is waiting for you to give it a command or a program to execute). It also give you three indicators (suggestions), what you can do. As you probably don't have knowledge of Unix, my advice to you would be to type the last one (exit) and enter.

The system would try to boot in the more familiar (to you) format.

I would rather suggest that you try and boot into Safe Mode first and see if you can get it to boot there, than starting at the command line. When you are in Safe Mode (Means holding down the SHIFT button while restarting), we can assist you going further. If it does not want to boot into Safe Mode, tell us that too.

Leo

When in Single User Mode:

Right after the root# prompt, enter the following:

/sbin/fsck -fy

Press the Return key.

You’ll see the prompts as each part of the hard drive’s directory is checked. (Checking extents overflow file, Checking catalog file, Checking multi-linked files, etc.) It will take a few minutes. At the end, if your drive was OK, the screen will say “The volume (name of your hard drive) appears to be OK”. If any repair was made, you’ll see the prompt, “FILE SYSTEM WAS MODIFIED”. Then, you’ll see the root# prompt again.

Right after the root# prompt, enter the following:

shutdown -r

and the Mac should reboot.

From your pictures it seems however that the Mac cannot access the drive. Do the AHT as in Apple: Hardware Test

You can also try to work through this guide, to try and solve it: follow the instructions for ML /Mavericks.

..Step by Step to fix your Mac | Apple Support Communities

Finally, when all this fails: Boot your Mac into the CC copy that you have and try and repair the internal drive from there.

Leo

Edit: When you are in the Recovery Mode, try with DiskUtility to fix the drive. Before the drive is not fixed, you will not be able to install or re-install. First get that sorted out.