iMac G3 recognized and installs on new hard drive but won't boot.

So your first partition was smaller then 8 gig?

When you boot and hold option down does it show up?

 

It's probably formatted with the wrong partition scheme. PowerPC Macs require an "Apple Partition Map" partition scheme. If it's the wrong partition scheme, it'll install no problem, but won't boot. Pop in the install disk, go to disk utility, select the hard drive, click the partition tab, then change the number of partitions from "current" to "1" and then click the options button below and make sure the drive is set to partition as Apple Partition Map. Then format the drive as usual. That should solve your problem.

 

Mac OS 9 won't format a disk with GUID and it will only install onto one formatted with AMP.

 

Ah, I misread the post. For some reason I was thinking OS X, not OS 9. The main reason I guessed the partition map was the problem was because I recently had that happen on my PowerMac G4 when I installed a 1TB HD that used to be in my Mac Pro. It installed Leopard no problem, but refused to boot.

 

Maybe your new system folder isn't properly "blessed." I don't know exactly how to do that, but you can google it or maybe others will have suggestions. Other than that, the only thing I can think of is to run Drive Setup off the install CD, highlight your hard drive and from one of the pull-down menus (I forget which one) select Update Drivers.