Mac Pro won't start after bootcamp partition

I have just used Bootcamp to place a partition on my MacBook Pro (2.5ghz 2008) and install Windows 7 ultimate x64. Whilst in Windows for the first time, I ran the windows support software (windows drivers for mac) from a DVD. I then allowed 2 windows updates to complete before choosing to 'Restart' my computer. My computer shut down and has been able to start since.

When I press the power button, the light on the button at the front (which opens the latch for the lid/screen) shows but then disappears as the power button is released. If I hold my finger on the power button for longer, the light stays on and you can hear the drive starting up, but this only lasts several seconds before cutting out again. The screen remains black the whole time. It doesn't matter if I hold option, command +R, etc, it just dies as soon as I release the power button.

I have poured through numerous Bootcamp problem posts but have been unable to find a solution.

Any help would be greatly appreciated!!!