Possible reasons why a computer is not able to start normally after a sudden shut down?

There are too many reasons but now you must resolve it ......so try to start your computer in a safe mode ...........................if it was caused by a software 

There are too many reasons for this problem, but most probably it cause hardware failer or some operating system files have been crashed or corrupt.

the problem of RAM

or Harddisck

WHEN SHUTTING DOWN THE COPMUTER SUDENLY SOME OF WINDOWS FILE STILL WORKING , AND MABY IT DAMAGE SO THAT IN NEXT TURN ON COMPUTER THE COMPUTER NOT WORKING NORMALLY BEACUSE THE WINDOWS OS WANT TO MAKE SURE IT DIDNOT LOSE ANY SYSTEM FILE