Some monitors are simply not Linux compatible.
My girlfriend has a weird Chinese-made monitor and it doesn't work under Knoppix. Knoppix tries to get a good screen refresh rate, and it just fails.
X windows doesn't appear, and Knoppix is just unusable with it except in text mode.

I'm guessing that you had a non-standard monitor, and if it was CRT and unsupported, Knoppix may have given the monitor a thrashing as it went out of sync to find a suitable Xwindows setting. In some cases, throwing CRT monitors into weird frequencies can actually break them. This doesn't happen with true TFT monitors though. Try booting up again and when it seems to have stopped, try pressing Ctrl+Alt+f2 to try and drop into text mode.
If you are getting text mode and a command prompt, then it's probably safe to assume that your monitor is unsupported.