My wife's Macbook Pro just started having startup problems. After
pressing the power button, it only gets the the folder/flashing
question mark screen.

Before I get much farther: we bought the 'book used, and the seller
put a Solid State Drive inside, rather than a traditional hard drive.
It has worked fine the whole time we've had it (until last night).

First, I tried running Disk Warrior. It couldn't see the drive,
either. I took apart the case, rechecked all the drive cabling (I
noticed the four screws + "tires" that hold the drive to the frame
were NOT installed). A cable appeared loose/disconnected, though no
idea if it really was before that, or if my removing the case did it.

Anyway, tried powering back on before reassembling, and everything
worked fine, so I shut back down and re-assembled. I tried turning on
again, and we were back to the folder/question mark.

Tonight, I took it back apart, and at the same time, robbed a set of
screws/tires from an old Powerbook G4 to make sure the drive would
remain secure inside the case, just in case it was a connection
problem. I plugged/unplugged all the drive cables. None appeared loose
this time (though one appeared not fully-seated), but checked them
all, secured the drive with the screws/tires, and, as with last night,
started up before I reassembled the case and it started fine. Then, I
put the case back together and we're back to the folder/question mark
again.

I didn't see any obvious connection problems while I had the case
apart. Nothing really obvious is leaping out here to me. It would seem
logical that this is some sort of hardware problem. Is it possible the
problem is with the drive? If not, anybody got other ideas? I know the
SSD wasn't brand new, but I think it was manufacturer refurbished, and
the seller enabled TRIM.

Anybody got any ideas? I'd really like to get this fixed for my wife, but don't like the thought of having to totally replace the computer (or do an expensive logic board replacement) for a machine I only owned less than six months.