problem with Classic

I have just tried to restart my old iMac desklamp type that normally runs 10.4.? in classic os9. I can only get it to do a partial start up w/chimes then just a gray screen.
I tried holding down the on button to shut down and then start up again but still only a gray screen. Can anyone tell me how can I just get back to osX so this computer will be functional again?

Do you still have your Tiger (OS X 10.4.X) disks?

Thanks for the reply. Yes, I do still have the discs, however, my CD drawer would not open or I might have tried starting up with one of them. I ended up searching all over the net using another machine and found, finally, that If I did another cold start while holding down the X key, I would start up in osX. NEAT! I am relieved because that is my wife's computer and I was just messing around with it.
Again, thanks anyway.