MacBook Pro cannot detect internal HDD/SSD

Hi,

My Macbook Pro 13" (Mid 2012) cannot detect internal drives.

I swapped the HDD for an SSD a couple of years ago as my MBP was running really slowly. It's worked completely fine since then until this morning when I got a 'folder with a question mark' icon on start up. I've read various forum threads and followed the steps to try and fix that but they haven't worked.

I replaced the SSD with the original HDD again today and still get the same issue (implying that the problem is not with the SSD itself.

I have now connected the SSD externally with a USB-SATA cable and the laptop boots. Disk Utility is unable to see the internal HDD.

What is likely to be the issue here? Will it just be a problem with the cable connected to the hard drive internally (and if so is this simple to repair) or could it be a wider issue?

I haven't opened up the device for years so I can't see that I'd have managed to damage the cable between last night (when the laptop worked) and this morning.

Thanks in advance,

Tom