I just discovered that it's nothing to do with memory thrashing or anything else I might have mentioned, it appears I was the victim of the 'bad startup' bug that I've always suffered from. Maybe 1 out of every 10-15 starts of TR from Glidos never completes -- the DOS window just sits there doing nothing after the usual startup message. I have to manually close the TOMB.EXE from the taskbar and try again.
I wonder if the black screen is something to do with that? I don't know what the bug is -- I've had it ever since I started using Glidos. At first, I thought it was something to do with my Tomb Raider CD having a scratch on it, but now I use a mounted BIN image, and it still does it.