Thanks for the info, that's weird as I could have sworn that I'd seen in the past about doing via USB but couldn't find anything when I looked the other day. Was probably too cross at the time!
BUT, bizarrely, after about 2 hours+ of going through all the possible menu items, checking, double checking, changing things, changing things back, swapping cables and screens etc all to no avail, I eventually plugged it all back how it was, and it was suddenly fine again!
I was furious, but relieved. I wouldn't have minded but no-one had changed anything when it went wrong. We were literally sat watching a film and the screen went blank, while all remotes were on the coffee table away from kids' meddling fingers.
Makes me worry that the HDMi module is starting to fail maybe. As I did have trouble also with the STR-DN1030 making the screen go off every now and then for 5-10 seconds at a time and ended up just replacing it with a new pioneer vsx933.