I'm getting an image of a folder with a question mark in the centre upon start up - has my hard drive crashed??

There is a fair chance the hard disk drive may have errors, issues, damaged files

sectors not reporting correctly, and the content may be lost if you did not backup.

• If a flashing question mark appears when you start your Mac -- Apple Support

(read through the above support article, and note links at the bottom about OS X
Recovery and about Time Machine; consider a rotational hard drive is a moving

part & subject to wear, so a replacement after a few years is likely a remedy.)

You could attempt a rescue by use of Disk Warrior or some other known third party

disk utility however the base cause may still remain if you were to repair the kinds

of read error issues that cause the symptom. A new drive is advised. Also if you

can prepare the new one and install it, later the old drive may be accessible as

a storage drive, if in an enclosure or by use of universal USB drive adapter kit. It

need not support booting as a system for some files to be extracted or recovered.

A regimen of backup components external to the computer are advised to have

on hand and use, in addition to separate ones for Time Machine, clones, & etc.

In any event...

Good luck & happy computing! 🙂