Windows 7: Screen won't wakeup on reboot but computer boots without it!

If I reboot my desktop goes thru the procedure but the monitor stays black - nothing, not even the safety screen and no cursor. There is an amber light on the monitor which goes green when it receives its wake up call but it remains amber. I have to switch the power off entirely before switching it on again, and rebooting and this time the screen works.
I've run scandisk, I've gone thru scannow, I've installed the latest graphics card drivers. I've tried changing the power settings.
Bear in mind that this set up and computer has worked perfectly for 2 years and as all the hardware is working I believe it to be a software issue.

If you're using HDMI, try hooking up via DVI, or vice-versa. If you're using VGA, check all the pins on the connector, both at the vid card and at the monitor.