Yep, unplugging everything for about half an hour has worked for me, too, in the past.
Same thing happened to our TV last week, ( nothing to do with a computer, just a TV and adjacent decode box plugged into it. ) nothing I did removed the No Signal message until .... went to bed in frustration, pulled the TV ( only ) plug out of the wall and in the morning the TV worked perfectly as if nothing had happened.
I guess this is Harold Wilsons " White Hot Heat of Technology " ( for those in the UK who may remember that remark )
Should mankind have invented the wheel, I occasionally ask myself ?
Town Criers of the World - Unite.