While I don't think I physically push the tray in during booting, I probably pressed Eject at the "wrong" time. I'm surprised that this could cause trouble, however.
Ah well. None of the stores around here sell CD-ROM drives. The ones they sell either read DVD as well or are writers. Either way the price is a little higher than I had hoped - but really quite cheap in an absolute sense.
Thanks for your comments.
sc