Hi there and welcome
Can you hold the power button down on the Mac until it turns off.
Then hold down SHIFT and with it held down, power on the Mac and keep Shift held down until it loads.
Tell me if it then starts please.
ok, can you do the following please
Tell me please if it then starts.
Shift is the one you use to type CAPITALS (the up arrow), control is CTRL and Option is the key with either OPT or ALT on it.
But you had to press these (command and Option) in my last instructions. Are you sure you did my last instructions correctly? Just need to confirm.
ok, then we attempt this please (we are going through and eliminating all causes for this problem)
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.
Let this complete and when it has, tell me if you still have the problem please.
Thanks, ***** ***** the problem and luckily it is not the hard drive but the Ram or motherboard that is at fault, your data is very likley still safe
I am really sorry about this and you are going to have to return the Mac to have a diagnostics run and the faulting component replaced. It will be covered by the warranty if this has not expired, and the replacement will be done at no cost to you.
I am really sorry about this, and if you have problems, or would like any additional information or assistance, please do not hesitate to let me know.
And if you can take a second to rate my service, that would be greatly appreciated.