What does the label on the Panther disc look like? Is the label black with a large white X on it?
If you are trying to upgrade your G3 with a model specific disc rather than a Full Retail version of Panther, then you would have major difficulties .... The model specific Panther Install Disc is only designed to work with the very model that it was released with and the OS version that originally came with your G3 (if I have the right model) was Mac OS 8.5.1.
So basically this means that your mac was released prior to the release of Panther and so you need to source a Retail version of the Panther OS. I did exactly what you are trying to do quite recently and found a Retail Panther
(full version NOT an upgrade version which requires you already have OS X installed) on eBay for a decent price.
Is this your G3?
This is extremely important and I need to verify that you have downloaded and installed the appropriate Firmware Version for your G3 before proceeding with the upgrade to Panther.
See this link.