No bootable disk detected ...!!!

I have a Macbook pro mid 2012 model with i5 processor and 4 gb ram (already bought rams for upgrading) , i was using the browser and closed the laptop lid as always without shutting down , and left it in its pouch and to my shock , while opened next time for use found the command saying 'NO BOOTABLE DISK ' on black screen , i have been using windows using bootcamp and by default the windows was used for booting , i tried all the ways like doing PR reset and trying to go to recovery mode but none helped as I cannot see the internal disk which is connected even in disk utility and even tried going to terminal and using diskutil list and still the harddisk is not detected now i am using a external disk for booting into my laptop , I also noticed that while i was trying to use it after closing the laptop lid that ,my mac was extremely hot , Does anyone have a solution for this , I am already freeking out as i am student and I have a lot of documents and files on my mac , Is there any solution , THANKS IN ADVANCE ....!!! fellow macmates ...!!!

(very unluckily i already ordered ssd upgrades and ram upgrades for my mac and now i am confused ) Desperate cry ...!!!!