Not able to reinstall OSX

My Macbook Pro froze couple of days back and did not restart (Grey screen). I had upgraded to the latest Yosemite.I tried Command-R, Comman-Option-R to reinstall. The screen comes with 4 options and when I press reinstall. OSX Mountain Lion comes up (Guess that is what came preloaded). Unfortunately after agreeing to the T&C, the system is not able to identify my hard disk and is getting stuck. I repeated the same a few times, once or twice it found my hard disk, but while reinstalling midway it ges stuck and I am back to square one.

I did Command D to check for hardware problem and Apple diagnosed "No trouble found".

I tried to reset PRAM (command-option-P-R) nothing happened.

I think the basic issue is the system is not able to locate the hard disk at times.

How do I reinstall OSX. I already had backed up my data so data loss is not an issue. I just want to reinstall OSX.

Any help will be greatly appreciated.