I've been searching for an answer to this particular problem for a while. Sorry if I missed a previous thread. Last month, I bought an early G5 (1.8 GHz Power PC) from a coworker. He wiped the HD clean and installed the original OS -- 10.3. After sorting out the upgrade to Leopard, and resolving the Flash issue, the HD started acting up. Sometimes the G5 would recognize the OS, sometimes it wouldn't. It would always recognize the install disk. Thinking that it might be a HD issue (and wanting additional space), I bought a WD 320 G HD and went through the process again. I've finally got it fairly stable, but there's one more issue I can't resolve. At random times within the first 1/2 hour of starting up every day, the HD stops spinning. I've been able to get it going again by unplugging the HD harness and plugging it back in, which I know is not good for the HD. After one or two or three times, it runs fine for the rest of the day. I've tried using the lower slot and harness -- that doesn't work at all. Also, I had IT at work plug both HDs into machines at work -- they both work fine. I've checked the harnesses -- there's no apparent fraying and they are connected firmly. The only thing left is the motherboard...but why would it cut out and then work fine after unplugging and reattaching the harness a few times? That doesn't make sense to me. Any insight would be appreciated. D.