yYour friend could try and boot it in diagnosic mode and do a full hardware check (If i recall right you shut right down, then when you power it back on press and hold the D key) . It can take a while.
If there is an error it will iwht a format like like 4MOT/2/40000004:0x3cc5BF90
If he gets an error code, call the friendly *** at AppleCare and they sould be about to tell what the code is if they can be bothered to look it up.
(or they will just tell him to clear the PRAM to get him off the phone 😡)