I am now getting kernel panics reproducibly after having replaced an internal hard drive, but only with two drives connected, as in the previous working configuration. My system: 400 MHz AGP G4. It had a 10-GB Maxtor internal ATA + 40-GB Seagate internal ATA (the boot drive with System 10.3.9). The Seagate was showing frequent errors, so I decided to replace it with a 60-GB Western Digital drive I had on hand. First, I temporarily removed the 10-GB Maxtor, installed the 60-GB WD in its place on the terminal connector of the ribbon cable, with the 40-GB Seagate on the middle connector (the other terminus to the motherboard). Disk Utility initialized the new drive, erased it, and verified that it looked OK. I then used CMS Products' BounceBack Pro to copy the entire old 40-GB Seagate's contents to the new 60-GB WD. That copying seemed to go fine. When I temporarily removed the new 60-GB WD, replaced its position in the bay with the 10-GB Seagate that I want to keep, and placed the new 60-GB WD into the top slot of the bay (middle cable connector), the system gave kernel panics even when booting from the OS X 10.3 installation disk. Sometimes those came before anything booted, sometimes after Disk Utility was started from the CD though ti could never get far. I checked the four RAM modules (one each 64, 128, 256, 512 MB) and removing each did not prevent the kernel panic. What did prevent the kernel panic was removing the last drive on the cable, at this time the 10-GB Maxtor. With that connector removed, everything booted fine. Next, I could place the cable's middle connector on the 10-GB Maxtor, and it would boot from that drive fine. Whenever two drives were on the cable, kernel panic. So, bad cable? I bought a new ATA/IDE cable for dual internal drives, connected it onto the two drives, and same result: reproducible kernel panics when two drives are attached! Next, I tried a single-drive cable I had on hand: connecting only the new 60-GB WD gave a kernel panic. Replacing the cable with the original dual-drive cable, but connecting only the new 60-GB WD on the middle connector: everything OK. TechTool Pro 4.0.3 says all the hardware is fine. Disk Utility and Norton Disk Doctor say the software on the drives is OK. So what happened that I can no longer have two drives on the cable without getting a kernel panic? I'd like to use the 10-GB Maxtor if possible, though it's not critical because I backed up all its files to the 40-GB Seagate before copying that to the new 60-GB WD.