PS3 - Power on, no sound, vision or HDD activity

DuckStab

I've tried posting this in a few places to no avail, hopefully I'll have better luck here. Apologies in advance for the lengthy read!

I have a launch day PS3 - 60GB CECHC03 - and apart from an issue with the lens years ago, it's been working fine ever since I got it but started giving trouble a while ago.

When I started playing The Last of Us back in June it would shut down without warning anywhere between 30 seconds to 10 minutes into the game seemingly with no reason. I would get a triple beep and a flashing red light, but the console would start straight back up if I pressed the power button.
The only other game this happened with was Uncharted 3, but as they were both Naughty Dog games I figured that was the reason.

Anyway, I shelved TLoU and went back to playing other games, none of which ever crashed. All was well up until October when I was playing Dynasty Warriors 8 when all of a sudden the display froze, but the background music etc. kept playing. I tried turning it off via the controller but there was no response, so I held down the power button on the front until it went solid red.

Now every time I try to start the console up, the green light will turn on (and the blue if there's a disc in), but there is no sound or vision.

It seems the main issue is that the HDD light will only flash for a second right on startup, then there is no activity thereafter. Whereas when it was working normally this would constantly flash during the startup procedure. When I got the console initially I upgraded the HDD to 500GB but I also kept the original 60GB just in case. I've switched HDDs but the result is the same.
As it is now, to shut the console down I have to hold the power button for about 10 seconds instead of the usual 2-3. But is is still just red or green, I've never gotten the YLOD.

I had the problem of no vision once before when I had to switch between AV and HDMI cables but this isn't the problem, because I have sound being output through the optical cable and the last time it happened even though there was no vision there was sound. But to be sure, I changed the cables and had the same result. The TV does detect that something is connected because when I have the console off "Check cable" is displayed, but this changes to "No signal" when I turn it on.

Also, my controller will not turn on the console or synch with it. When I press the PS button the 4 lights just flash continuously like it's searching for a console but turn off after a while. When I connect it to the console via USB it will charge it, but pressing the PS button will not do anything.

I've tried entering Safe Mode, and despite the console actually beeping at the correct intervals there is still no onscreen activity.

I e-mailed PS customer support and was told to ring them, I rang and simply got told to go through Safe Mode again. I was hoping to get it repaired through Sony but apparently I can't, which is disappointing considering they repaired the console several years ago when the lens needed to be replaced.

I know I can just get a replacement slim console fairly cheap but I'd like to keep this one alive because it's one of the few with PS2 backwards compatibility. And sentimentality too, I suppose.

As regards a replacement, I'm probably going to get a 12GB slim and use my old hard drive, but does anyone know if this might cause any issues? I was reading that the 12GB is flash rather than HDD so would putting in my 500GB with all the old game data/saves etc. conflict with this? Would it have to be formatted before use?

Anyway, hopefully someone has an idea of what might be causing the problem, and if there are any possible fixes out there, thanks!