Red X after HDD, screen and jack replacement

Good evening all,

I'm having some trouble with my 80GB iPod Classic.

Here's the story: I started by replacing the screen as the original was covered in scratches and dead pixels.

All was well, almost.

(I think) I was a little careless during the reassembly and must have inadvertently damaged the earphone jack assembly. It worked totally fine, however a few days later I lost audio in one of my earphones (note this iPod has had two jack/hold replacements in it's long life, though they were performed by a third party company) this whole ordeal was the first time I've tinkered with it myself.

So seeing as I'd replaced the screen myself I thought I'd have a go replacing the jack/hold. Which I thought was fine.

During the process I disconnected the hard drive as I was automatically in screen-replacement-mode and totally forgot that I was following different instructions. When I finished this reassembly I was faced with the dreaded circled red X. As I've had an issue with my hard drive in the past (previous red X during use, banging it off a table fixed it) I assumed it's time had come and I have purchased a new one. This replacement also resulted in a red X.

Performing a diagnostic shows everything is fine except for the HDD, which cannot be opened. "[Can't Open Device] ERROR! Diag Halt"

The ribbons seem to be connected fine, though I have noted that the problem has only been around since I disconnected the HDD from the logic board during the jack replacement. Could this be as simple a fix as me just not doing something quite right with the ribbons? I can't for the life of me figure out what else it could be.

Any help would be hugely appreciated.

Thanks,

James