I was going to try unplugging the extra 4 pin power connector at top of MB ...as heard its not really needed....worth a try as did not have that on my other board.
Don't what you read isnt always true, it is needed. DOCP problems have been resolved directly by plugging both in and fair few other issues. BOTH is best and 100% certain this is not source issue for you.
Just does not start up... case switch could be sus, try onboard on/off and see if this works. However if you must turn off power supply this normally indicates a dead short condition or even over-voltage / something is tripping PSU protection mechanism.