I'm sorry if this isn't the best in question response, despite a little tipsy being a friday night... The whole pc was shut down, including monitor. No sound coming from the head unit, while that remained on, and a blank touchscreen. There was no 'No Signal Found', etc, on the monitor and no sound running through the headunit/speakers. I am basing this on the fact that I had to power on the pc again, and switch the monitor on (sorry I didn't mention turning the monitor back on in the original post)...
Oh, and abut the monitor - if you take a look at the original post, the computer was indeed shut down, not the monitor. Or not just the monitor - that's not clear from the original post.
But if you want to test, stick to the OP's set up - hence an M4. In fact, this is HIS test wrt his case.