Trying to erase hard drive

I have an old Mac G3. I'm currently running OS 8.6. I've been having trouble with lots of crashes, and the box on hardbooting says there are errors that the disk software cannot fix.
So, I've been trying to use the CD as a startup disk in order to erase the hard drive. But when I start from the CD I get a bomb message.
Is there another way to startup the computer other than the hard drive as startup?

thanks

[Moderator]

What bomb message are you receiving?

Try this:
Put the CD in
After you hear the Mac startup sound, press and hold the C key
(if that doesnt work, then try pressing and holding the C key and then starting up your Non-PC Macintosh)

And if, once again, that doesn't work, after the Mac startup sound, press and hold the SHIFT key
(Or try the same thing with the S key)

Try that, and let us know what happens