Hello, and welcome to JustAnswer.com!My name is Jesse, and I'm here to help.
Let's start by holding down just the Option key when it starts up.
Same thing. Gray screen and initial sound playing over and over. I found someone on Youtube with he same problem. Recorded here:
Okay, try holding down the Command+Option+P+R keys while you power it up. Hold those down for 3 restarts.
One last thing to try, hold down the Option+D keys while it starts up.
Okay, in that case you have a serious hardware issue. You'll want to visit your local Apple Store's Genius Bar, or a local certified Apple repair shop, so they can open it up and check the problem.