Persisting black screen on Xbox One, need help

Hi, I'm getting a constant black screen on my Xbox One with no picture at all, I'll run through what I have tried so far and try to include as much detail that I'm aware of as I don't know what the next step is to identify the problem. When I turn the console on, the power lights come on fine and can apply updates via USB (I get the correct sequence of beeps) but do not get a picture at any point.

It originally happened a few months ago where I would turn it on but not get any picture but I left the console for a couple of weeks untouched and it came back on fine apart from every now and again the picture would cut out for a couple of seconds to a black screen. After a few more weeks the problem came back and I've had no picture again.

Firstly, I have tried multiple TV's and HDMI cables but to no avail - still black screen and no picture (ever). I have tried different power leads and the console seems to be powering up fine.

I read online that it can be a common problem with the Hard Drive. So i plugged the hard drive into my PC and used HDAT2 to analyse it to check for errors - no errors were found.

So next step I formatted the hard drive and ran a windows script I found online to set it up correctly and applied the updates off the Xbox support website to the USB stick and hard drive.

When I turned the Xbox back on, it made all the correct sounds like it's applying the updates via the USB and it restarted itself after about 10 minutes which as far as I know means it's all working fine - but still no picture on my TV at any point.

What's my next step? I've considered buying a new hard drive so I can eliminate the possibility that its a hard drive issue but it seems to be working OK other than the picture.

Should also add it is 100% definitely in the correct HDMI port on the console and TV and it is the original Xbox One 500GB model.

Thanks for any replies it's really baffling me and just want my Xbox back!