I'm having a very serious problem which is making my installation of Tiger a complete non-starter at the moment. When I first inserted the DVD, it came up fine. I was browsing the documentation, when suddenly, (keblam!), the disc span down and the Finder went into eternal beachball mode. I rebooted the system and tried to insert the disc again. I got a message saying the disc contained no recognised partitions. I tried again, and it worked this time, so I launched the installer and clicked restart. My PowerBook restarted and the disc span up, made some rather nasty clunking sounds, and then span down again and was silent. The grey Apple logo appeared on the screen shortly after, but nothing else happened at all. I rebooted and tried the same several times, with the same result. Once I got as far as the circular progress indicator that appears beneath the Apple logo, but no further. I cleaned the disc by wiping it from the centre to the outside. It doesn't have any scratches, aside for a few small scuff marks that I'm pretty sure weren't there before I put it in for the first time. (I have a curious obsession with studying the underside of discs I'm excited about.) I don't have an problems using and playing CDs, except for very rare occasions when they seem to go crazy, and the same applies for DVD movies, which usually work fine if they are free of scratches. Tomorrow I'm going to buy a CD lens cleaner, to see if that makes any difference. Anyone have an opinion on whether that is likely to fix the problem, or if there is something seriously wrong with my Tiger disc, my DVD drive, or (unlikely but amusing to contemplate) both? I am tearing my hair out.