I had the same problem. It can be 3 Things !!!
1 = POWER SUPPLY ( Look on You Tube how to Identify this one. )
2 = APU Not Seated Properly. ( Send it in for Repairs or get a new one BAD LUCK - THANKS SONY !! )
3 = Full off Dust and overheating. )
Mine was No 3 !!!
Took off covers. Pulled out Hard Drive and Power Supply. Took it in to work and Blew all the $@$* out
of the PSU and Fans and Heat Sink. ( WAS REALLY DUSTY. )
Put it back together and worked fine ever since.
May not be the answer to all the problems but this helped mine. PS... KEEP IT CLEAN !!!. )
HOPE THIS HELPS SOME OF YOU GUYS OUT !!!!!