Same problem with different drives: DVDs aren't recognized

Question

I hope everybody's having a good evening. Here's my deal:
Shortly after buying my PowerMac G4 (MDD) in 2003, I put a Pioneer DVR-A06 Superdrive into it, and it was great. Eventually, though, the 4x DVD burning and lack of DVD+R or dual-layer burning proved insufficient for my needs, so I replaced it with a Pioneer DVR-112D almost a year ago. Everything continued to be fine until a couple of months ago, when suddenly, the drive refused to recognize discs. Any disc, be it blank or full, CD or DVD, would spin for several seconds before being spit back out. I ran a cleaning disc through the drive, which didn't help. I decided the drive had gone bad, so I replaced it with a Pioneer DVR-116D. Once again, everything seemed fine for a few weeks.
But everything is no longer fine, as of a couple of days ago. The Pioneer Superdrives I've used have always been finicky about discs; sometimes, discs rejected by the Pioneer drives would work perfectly in the PowerMac's original Combo drive (which I moved to the lower bay and set to slave, but have otherwise not monkeyed with), set-top DVD players, and my iBook's optical drive. But now neither the original Combo drive nor the brand-new Pioneer burner will recognize DVDs, and the Combo drive won't recognize CDs either.
This is a very sudden development: once the Pioneer drive stopped accepting DVDs (even blank ones! I can't burn anything either), the Combo drive stopped accepting any discs at all. I've run a cleaning disc through both drives (the Combo drive actually rejected it), and even opened them up to inspect the lenses for dust or scratches (they're pristine). The Combo drive is now five years old, so I'm not surprised that it's failing, but I'm now on my third Pioneer drive in just under a year, so I think something else is going on here.
Is it just that Pioneer makes really picky drives, and that the Combo drive just happened to coincidentally fail at the same time as the brand-new Pioneer? Is there some sort of hardware issue I'm not considering? Or is this a software problem of some sort? I've noticed some performance changes since installing Leopard (not unexpected, since it's an old, non-Intel machine); could it be OS-related?
Any help would be greatly appreciated. Thanks for your time and effort!

Answer 1

Hi, and thanks for your response! I'll try reinstalling Leopard.
My PowerMac is still very fast with Leopard, though the processors are having a noticeably harder time keeping up. Things get hung up more frequently than with Tiger, but not enough to really be a problem (I could certainly use more processing power for video encoding, but then again, who couldn't?). I also upgraded my MDD's video card, so I imagine the performance drop is all the more noticeable in machines that still use the original hardware. Regardless, my MDD handles Leopard much better than my G4 iBook, which went from flying with Tiger to crawling with Leopard.