Did you try following the instructions at the link I posted? You may need to take this PC to a reputable PC shop and have them test the PSU etc...
GOT A NOTICE OF 2 DELL UPDATES. CLICKED ON THEM AND 5 SECONDS LATER SCREEN WENT BLANK AND WILL NOT COME BACK UP. CANT REBOOT  ABSOLUTING NOTHING. TURN MONITOR OFF AND BACK ON. PRETTY SOON IT SAYS MONITOR GOING TO SLEEP SO MONITOR IS WORKING. TURN OF COMPUTER AND KILL ALL POWER FOR 10 MINUTES. TURN POWER ON HEAR THINGS START UP BUT NOTHING. EVERYTHING WAS WORKING GREAT ON THE 3650 BEFORE CLICKING UPDATE
2 UPDATES