I have a MacBook air - underside shows it's model A1466, but not sure what year it is. When I boot it, I hear the sound as normal but after a few seconds, I get a flashing folder icon in the centre of the screen, with a question mark on it. I've tried resetting SMC and PRAM. The PRAM reset seems to work fine except that the progress bar shows it's only halfway through after about an hour.
Any ideas as to what could be wrong? Does this mean it needs a new disk? If so, does this need a special SSD or will any SSD disk suffice?
Thanks in advance