Change of Monitor after installing Knoppix on hard disk

I've switched my old 21" Sony monitor with a Samsung SyncMaster 173S flat panel. After the switch, the quality of the display is not as desirable, so I decided to change the monitor setting through the control center. I saved the changes and reboot the machine. My nightmare started.

Now once I boot the machine, I have the message "Video mode not supported" message. I tried booting from my knoppix CD and setting the display to the lowest resoluation and refresh rate, hopping that I can get back to a good start and trying reseting the Monitor, but nothing works.

I read in this forum that I can use the "knoppix" command. But I can't find the path to the command. Can somebody please help? thanks!