10.5.8 grey screen

my mac has got stuck on the grey screen with a question mark so I put in leopard 10.5.8 disc and turned it on

holding down the c key this worked 3 times but now the screen comes down like a curtain and tells me I need to restart the computer and does the same thing again. The disc is still inside and I've tried the usual suspects holding down the mouse, or c button but nothing works.

Any suggestions anyone?

Thanks