Q: MacBook Pro frozen in OSX installation

Your information is a bit unclear. I think you need to do this: Shut down the computer by pressing and holding down the Power button until the computer shuts down. Restart the computer. Now, exactly what happens when you do that?

What OS version is on the computer now? I don't really know because you say your model is a 2011, but you've posted in the 2006-2010 forum. Do you have data on the drive you need that isn't backed up?

Install or Reinstall OS X from Scratch

Boot to the Recovery HD:

Restart the computer and after the chime press and hold down the COMMAND and R keys until the menu screen appears.

Erase the hard drive:

  1. Select Disk Utility from the main menu and click on the Continue button.

  2. After DU loads select your startup volume (usually Macintosh HD) from the

      left side list. Click on the Erase tab in the DU main window.

  3. Set the format type to Mac OS Extended (Journaled.) Optionally, click on

      the Security button and set the Zero Data option to one-pass. Click on

      the Erase button and wait until the process has completed.

  4. Quit DU and return to the main menu.

Reinstall OS X: Select Reinstall OS X and click on the Install button.

Note: You will need an active Internet connection. I suggest using Ethernet if possible

           because it is three times faster than wireless.

This should install the version of OS X that you had installed.

Yes, it will. You did not say anything, so I thought you were OK with this. If not, then you can try this first which will not erase anything:

Reinstalling OS X Without Erasing the Drive

Boot to the Recovery HD: Restart the computer and after the chime press and hold down the COMMAND and R keys until the menu screen appears.

Repair the Hard Drive and Permissions: Upon startup select Disk Utility from the main menu. Repair the Hard Drive and Permissions as follows.

When the recovery menu appears select Disk Utility and press the Continue button. After Disk Utility loads select the indented Macintosh HD entry from the the left side list.  Click on the First Aid tab, then click on the Repair Disk button. If Disk Utility reports any errors that have been fixed, then re-run Repair Disk until no errors are reported. If no errors are reported click on the Repair Permissions button. Wait until the operation completes, then quit Disk Utility and return to the main menu.

Reinstall OS X: Select Reinstall OS X and click on the Continue button.

Note: You will need an active Internet connection. I suggest using Ethernet if possible because it is three times faster than wireless and more reliable.

Alternatively, see:

Reinstall OS X Without Erasing the Drive

Choose the version you have installed now:

OS X Yosemite- Reinstall OS X

OS X Mavericks- Reinstall OS X

OS X Mountain Lion- Reinstall OS X

OS X Lion- Reinstall Mac OS X

     Note: You will need an active Internet connection. I suggest using Ethernet

                 if possible because it is three times faster than wireless.

If the computer won't startup, then you cannot backup your files without first replacing the drive or trying to access it from another Mac using Target Disk Mode if your computer has either Firewire and/or Thunderbolt ports.

If you must start from scratch, then:

Install or Reinstall OS X from Scratch

Boot to the Recovery HD:

Restart the computer and after the chime press and hold down the COMMAND and R keys until the menu screen appears.

Erase the hard drive:

  1. Select Disk Utility from the main menu and click on the Continue button.

  2. After DU loads select your startup volume (usually Macintosh HD) from the

      left side list. Click on the Erase tab in the DU main window.

  3. Set the format type to Mac OS Extended (Journaled.) Optionally, click on

      the Security button and set the Zero Data option to one-pass. Click on

      the Erase button and wait until the process has completed.

  4. Quit DU and return to the main menu.

Reinstall OS X: Select Reinstall OS X and click on the Install button.

Note: You will need an active Internet connection. I suggest using Ethernet if possible

           because it is three times faster than wireless.

This should install the version of OS X that you had installed.