Why can't I instal Leopard on my PowerBook G4?

At a guess – how old is your computer? how large is your hard drive? Is it possible or likely that you did an Archive and Install when you installed Leopard for the second time, and ran out of disk space?

fsck is your friend. Go here and do as Apple says!

Were you using Unsanity’s Application Enhancer on Tiger prior to installing Leopard? There was a known issue where installing with APE installed would corrupt the Leopard installation. Happened to me with a G4 Powerbook and my C2D iMac.

As cwilber asked, Leopard can’t be installed on machines slower than 867mhz, so if it’s a Titanium PBG4, it might be slower than that.

Yeah, good call, it’s probably the Application Enhancer conflict, but most people (including me) don’t know 1. what that is or 2. how to get rid of it. blunkhouse, do you have a link to how to fix that problem?

Here’s Apple’s “official” fix for the Unsanity APE error:
http://docs.info.apple.com/article.html?artnum=306857

There is plenty of information out there. Just Google Leopard and Unsanity and you’ll find hundreds of articles about the conflict.

Hope this helps.

No my HD is completely free, no space occupied. Secondly, Leopard has worked on this computer before.

My guess is your hard drive is beginning to bite the dust. I’ve heard of “journaled” hard drives masking significant problems. That’s why I suggested the Apple support article that walks you through booting into single-user mode and running fsck until your disk has no more errors.

Fixed it by installing using target mode and an iMac. The combo drive was too slow to read the install according to the people in the apple retailer I talked to. Thanks for your help guys!