HELP! I switch on my mac pro and the monitor cycles through analog/digital a few times and then "check video signal" pops up - I can't seem to display anything.! The mac was working just fine until about 1 hour ago - i had to restart for soemthing and now I can't get any video signal at all? What has happened? I can't think it'd be the cable as it was fine until 1 hour ago I have taken the card out given it a clean and placed it back in a new slot on the motherboard but still nothing. help appreciated - this is urgent I need the machine to work!