Thanks go out to several LJ folks who kindly pointed me at pages upon pages of good information about troubleshooting my XBox. I learned lots.
The symptoms I’m experiencing point to three possible root causes:
1) Overheating. This is the most likely, because for the first year or so of use the XBox lived inside a glass media cabinet, and it got H-O-T HOT in there. I suspect that there are temperature-sensitive components that have now degraded and are performing unreliably, but none of the pages I read (or at least was capable of understanding on first skim) indicated WHICH components I should be concerned about. The suggestion was to open the console, dust everything out with compressed air, and keep it in an unobstructed cool place. It’s been living in an unobstructed cool place for the last three months, so I doubt disassembly will help much.
2) Bad DVD drive or dirty optics. Some of my symptoms correlated EXACTLY to this, so I bought (oh, the budget pain!) a lens-cleaning disk at Walmart. Yes, it’s a “dry” kit. They had no wet ones. I ran it last night, and then we watched a DVD with no trouble at all. Granted, one DVD does not prove anything, since the problem has been intermittent. Besides, we tried playing DDR Ultramix 2 again, and it hung on the “don’t fall off the playing mat” warning screen.
3) Bad HD or corrupted data on disc. Some of my symptoms correlated to this, so I followed tech support’s instructions and deleted all my game saves and rebooted. No joy: DDR is still broken.
The upshot of all this: if we want to get the $90 worth out of our DDR purchase, we’ll have to spend another $90 on repairs (that includes the shipping) and do without DVDs or XBox games for three weeks, or we can spend $150 or thereabouts on a new XBox, in which case we’d then have TWO controllers and a spare XBox for cannibalization should I feel ambitious at some future date.
Nintendo has Appled themselves. Their hardware is obviously superior to their competitors — our Gamecube has been trouble-free and crash-free for three years, and our N64 has been beaten up to the point that the I/O jack needs jiggling before it’ll display, but it still plays games just fine. Hardware superiority notwithstanding, I can’t get DDR or Fable for the GameCube, and that’s only the beginning of a long list of games that will never run on a Mac… er, a Nintendo.