Check the power ribbon. I repair these all the time and most of the time I have found bugs have been in there and left feces behind on the power ribbon which eats into the plastic. Yes bugs fecal matter does eat into the power ribbon and I have replaced or cleaned 50 or so that had this problem. I even found a spider leg shorting out one of the bare ends where it plugged into the RF board. Inspect the cable and Clean both sides well and put it back in, sometimes works. Other problems include USB, the RF board and as stated the hard drive. I have only seen one that had a blown resistor on the board out of 50 or 60 I have repaired. It's almost always something simple. Thomas; You can get the power ribbon for $4.50 on eBay, its always worth a try since it worked when you replaced the RF module it stands to reason it's something to do with the power ribbon connection. Not the power supply, not the RF since you changed it, not the common USB short, all that's left is power ribbon or MOBO (and as I said that is a one in 50 chance).
I really hope this helps.