It's probably your video cable then
and it's plugged into the GPU
It happens to me too some time
Usually pluging it in and out does the job
sometimes I switch both ends
it was working fine this morning tho
and i did replug everything
I'll try switching the ends of the display cables
I've tried resetting BIOS (I think that's what the button did) and still nothing
because everything turns on
Do you have integrated graphics in the CPU?