A 14" monitor? Sounds like Knoppix is working fine, but that old monitor isn't supporting the display resolution it's defaulting to, and the monitor is likely so old that it doesn't have plug and play capability to inform Knoppix of the resolutions that it is capable of. You might want to look up the cheat codes for resolution and try a low resolution and a scan rate within that monitor's range. I suggest that you get the model number and look up what the relic is capable of. I also suggest trying a different monitor.