PowerBook G4 Start-up problem

Start-up problem ---
1. When I recently ran OnyX, I was told to run the Apple’s Disk Utility from the Start-up Disk.
2. However, before doing this, I ran the Disk Utility from the hard drive, but the program would not complete the “Repair” function. It just got “stuck” and I had to stop the repair.
3. While running the Disk Utility from the Start-up disk, I got the following message: “Disk Utility has lost its connection with the Disk Management Tool and cannot continue. Please quit and re-launch Disk Utility.”
4. I did quit and re-launch Disk Utility but received the same error message.
5. Took PowerBook to Apple store and technicians ran diagnostics (for several days), couldn’t identify problem even though computer wouldn’t start after they ran full set of diagnostics.
6. I reinstalled the OS 10.5 from scratch, reformatting my hard drive. Then, I re-installed all programs and documents, etc. Seemed to work OK.
7. Tried to run OnyX, but the computer froze. Ran Disk Utility from the start-up driver and it repair hundreds of permissions as well as “repair disk” function (hundreds of items).
8. While the PowerBook is running OK right now, am concerned about possible hardware failure.
Any thoughts/ideas?

Download Smart Utility from http://www.volitans-software.com/smart_utility.php . It will enable you to see the values of the SMART sensors, and can give you insight into the health of the drive.
When you ran repair disk from the OS X DVD, did it complete normally? No 'failure on exit' message?