Paul and Mike -
Thanks for the suggestions guys - but it seems to go from bad to worse!
The B-D advisor on the Cyberlink disc didn't recognise my CPU (Core i7- 3770, btw, not 3550 as per OP - sorry), nor the Intel HD4000 graphics.
Checked on C/Link website and found there's a later version of the B-D Advisor, supporting Windows 8, so I d/loaded and installed that. Took 3 tries, btw, to d/l the 37.42 MB file at 12-15 kB/sec.
Just as the installation finished, I noted a d/l coming in from LG, which installed itself and updated the firmware on the drive, to 10.01.0712.01. Don't know what the original version was - I'd looked but couldn't find it.
Ran the new Advisor - success! my system passed every category, both basic and advanced.
Put my first ever B-D disc in, one of the Prof Brian Cox ones, and got this message -
"You must update C/Link PowerDVD to continue the playback of this content". I clicked on Yes but tbh I can't remember what came up next.
Whatever it was, I did it, re-started PC, opened PowerDVD, box comes up "Loading ..." but almost immediately "Warning playback stopped because graphics card driver is incompatible ...Error Code = 0012, run the B-D Advisor tool for more info".
So I duly ran the advisor again, and the system again passed on every item, both basic and advanced.
Tried to play the disc again, this time I was invited to "update/upgrade" the s/w, so I clicked on the box and got the option of two paid upgrades or a free patch, a 42,548 kB file from C/Link, which I d/loaded and installed.
Started the player again, and once again I got the message "You must update C/L PowerDVD to continue the playback of this content".
Ran the Advisor yet again, this time all the Basic items passed, as before, but on the Advanced tab only 3 of the 6 items passed.
Just tried it again and everything passed - inconsistent or what?
Just fail to see why the disc won't play. CDs and DVDs play fine, btw.
Cyberlink are keen to sell me an upgrade to v.12 for under £30, which is cheap enough, but what's the point when their own tool tells me my system meets their requirements - but only until I try to actually play a Blu-Ray???
Anything else I can try?