Brought back power dead mac with following tip from Apple support.

I got a sudden power dead laptop overnight when left in sleep mode as usual. I couldn't get it start by any means and power connector was fine, battery was full etc.
I was pretty sure it was some hardware failure and was about to search Apple Service Centre however, while looking for address online found a toll free Apple support number and thought of giving a call to them.
To my surprise the call was picked up quickly and upon providing serial number and doing some rudimentary checks person on phone quickly asked me try 2 things first didn't work but second work like charm and it came back to life.  a 4-5 min call saved me a 2 hour trip to Apple Service centre and above all all this time I didn't have to hear the recorded sentences with unnecessary "Thank you", "Sorry", "Bare with me" and most importantly I wasn't made to feel like a dumb terminal on the other end.

Anyhow, apart from Rants here is the main purpose of the post to note down the tips.

Tip 1 :
Press   cmd+option+P+R and while pressed use Power  button to switch on Mac which in my case didn't work.

Tip 2 :
Press Right ctrl+options+space and then power button at same time, This worked in my case and my Mac came back on and started properly.

Upon asking what was the issue, I was told it was due to being a full memory and a software bug in OS that may cause it sometimes to appear power dead.  I didn't bother exploring technical details at that stage since I had other things to worry about.

I hope this helps me in future and some one else on the net to try it out first in such case.