Black screen when I try press alt key for bootcamp

I have noticed that when I boot normally the screen stays on illuminated black screen for 10 to 15 sec longer than it usuall before it boots into 10.6.8

When I press the alt key to select boot drive the mac just stays in this illuminated black screen, and i have to power down, holding the power button to restart. The boot camp did work fine for ages. The mac does not make the usual chime when powered on, whatever mode I am trying to boot into, and has not for a while.

Trying to boot into windows 7, its there in disk utility and if I re run bootcamp assistant, it asks me if `i want to remove the exsisting windows partition, which I do not want to do.

Thanks