Late 2011 iMac wont boot after Mavericks install
There are 3 more start ups you can try:


Press Option-Command-P-R until you hear startup sound a second time.
Press Command-V during startup. -Start up in Verbose mode. 
Press Command-S during startup. -Start up in Single-User mode.


here is more detailed information what to do.


  Start up your computer in single-user mode to reach the command line.
  Note: If necessary, perform a forced restart as described in the
  Emergency Troubleshooting Handbook that came with your computer. On
  desktop computers, you can do this by pressing the reset/interrupt
  button (if there is one) or holding down the power button for several
  seconds. On portable computers, simultaneously press the
  Command-Control-power keys. If your portable computer doesn't restart
  with this method, you may need to reset the Power Manager.
  
  At the command-line prompt type:

`/sbin/fsck -fy`

  
  
  Press Return. fsck will go through five "phases" and then return information about your disk's use and fragmentation. Once it finishes,
  it'll display this message if no issue is found:

** The volume (name_of_volume) appears to be OK 

  If fsck found issues and has altered, repaired, or fixed anything, it will display this message:

***** FILE SYSTEM WAS MODIFIED ***** 

  
  
  Important: If this message appears, repeat the fsck command you typed in step 2 until fsck tells you that your volume appears to be OK
  (first-pass repairs may uncover additional issues, so this is a normal
  thing to do).
  
  When fsck reports that your volume is OK, type reboot at the prompt and then press Return.


Your computer should start up normally and allow you to log in.

or see the link for more information.