Hi there and welcome
Whats the message you get when it fails?
Your doing the command + R when starting the computer?
Power off the mac
Then start the Mac and hold down the Command and R keys at startup.
Hold these keys until the Apple logo appears. After your computer finishes starting up, you should see a desktop with an OS X menu bar and an OS X Utilities window
choose Disk Utility from the Utilities window, or from the Installer menu if you're started from an installation disc.
Click the First Aid tab.
Click the disclosure triangle to the left of the hard drive icon to display the names of your hard disk volumes and partitions.
Select your Startup Disk (usually named "Macintosh HD").
Click Repair. Disk Utility checks and repairs the disk.
still the same error?
ok, is the computer starting at all? Or what happens when you try to start it?
ok, power it off
Then hold SHIFT and with this held power it on and tell me if it starts please.
power it off
ok, then the hard disk is faulting, and its likely to be a failing hard drive (hardware issue)
Your going to have to take it in sorry and have them remove the hard drive and try to get the data off it.
Then the drive will need to be re-formatted and reinstalled.
But as I do not want to mislead you, there is a good chance the data has already been lost sorry.
If you would like any additional information or assistance, please do not hesitate to let me know.
Else if you can take a second to rate my service by clicking one of the stars at the top of the screen then submit, that would be greatly appreciated.
No sorry as it cannot read the data, which we see via the repair.
It needs to be done by removing it and adding it as a slave drive into another computer.