well that was
interesting
Had a power cut yesterday and my second monitor stopped working. Checked on the web and general consensus was that it's fucked I'll have to get another one. So I thought I'd just try swapping monitor cables (difficult to trace which is which from the rat's nest at the back of the puter) , still fucked. I swapped them back and tried the monitor's VGA socket - luckily I still had a DVI-D to VGA adapter because it was originally set up as that but I'd converted to all digital to see whether it gave a better display (it had done, a bit).
Switched the computer on and still nothing on the monitor and my
main monitor also looked fucked, just a very faint Linux Mint symbol on the screen and I couldn't enter the password. So
main monitor now fucked, too
But hold on if it's displaying LM symbol it has to be working somehow so I switched the second monitor on and changed the input setting to VGA ... and it all works - that one was acting as primary which is why the LM symbol was greyed out.
So all working again