I have a G4 with OS 10.4.11. There were 4 internal drives, all working fine. I wanted to substitute a drive from an identical G4. That drive worked fine in the other machine. I brought it upstairs, tested it with a USB-drive cable, it was fine. I took out the sled (the one in the front) with two drives on it, took one out, put the new one back...and whoa! Neither of them are mounting. I tried re-starting multiple times, removing the whole sled and starting over multiple times, plugging and unplugging multiple times. No change. Disk utility doesn't see them. I ran "repair permissions" and "verify" on my system disk. It's fine. No problems. After I went to "system profiler" a couple times, it finally decided to "see" one of the drives, but gave it a weird name, "SP301A@E". But not mounted. Disk utility now "sees" that one drive, but all commands (including "mount") are greyed out. Bizarre. Obviously it's not the drives. I plugged and unplugged the ribbon cable leading to the computer a couple times. It's plugged in just fine, and looks OK. I must be missing something obvious. But what???