I finally found time to take a look, and it's much simpler than I thought (I didn't realise this until I'd already made it more complicated!).
The bolts in the front didn't need to come out at all, and there's a plate at the top of the front panel of the cabinet, which looked like it was attached to the amp, but wasn't.
Long story short, I got it open, sadly couldn't see any loose connections, so put it back together again. The screen still doesn't work, but the good news is that the amp still does.
I'll see if any local shops will take a look without charging the earth, but otherwise I'll keep an eye out for a Shortboard (which has its own screen), and carry on as I have been in the meantime.
Thanks for the advice everyone.
The bolts in the front didn't need to come out at all, and there's a plate at the top of the front panel of the cabinet, which looked like it was attached to the amp, but wasn't.
Long story short, I got it open, sadly couldn't see any loose connections, so put it back together again. The screen still doesn't work, but the good news is that the amp still does.
I'll see if any local shops will take a look without charging the earth, but otherwise I'll keep an eye out for a Shortboard (which has its own screen), and carry on as I have been in the meantime.
Thanks for the advice everyone.