MacBook Pro showing prohibitory sign on start up MacBook Pro with Retina display, OS X Yosemite. On the start up my MacBook Pro is showing a circle with a line inside which is prohibitory sign. It goes no further. Tried but the Disk Utility.
Stuck with my OS X Utilities for couple of days. I tried the Disk Utility.  Finding the way out.

I tried to do an Internet Recovery. 
Then I came to a window for install OS X. My current version is OS X Yosemite. I click to continue. It varieties computers eligibility, then I click agree to go forward. Next, it says select the disc where you want to install OS X. It won't let me install. 
What's that mean? 
Where is the problem? What to do?
You may need to erase the entire drive. Once you've booted to recovery, use disk utility to repartition your internal drive. 


https://support.apple.com/kb/PH20571
https://support.apple.com/kb/PH20567


Bear in mind that repartitioning the drive will erase everything.  If you don't have a back up of your data and every app (iLife/iWork are not part of the OS) that you want to install, repairing the disc might be a better choice.