Boots up but black screen

My 17" 2007 MacBook had the screen go black while I was working.

I rebooted holding down control alt shift I believe that was it and it came back on.

Now it's done it again. Power button turns it on front light comes on and slight screen glow near bottom.

Gives a single long shrill tone then the standard chime when power button is depressed. I can feel hard drive spinning seems to stop at usual amount of reboot time. But screen still dark.

Any help is greatly appreciated

Thanks! Ron