Monitor keeps blinking in knoppix LiveCD boot

[gopikrish]

After I pressed enter key in the boot window it said "You passed an undefined mode number.Press return to see video modes available, space to continue or wait 30 secs"
When I pressed enter it showed some modes and below there was "Enter mode number or 'scan' " So when I entered "scan", after monitor blinked for some time, another window (i think VEGA) with list of different modes appeared, this time when I entered "scan", monitor blinked for a longer time but same think window appeared again showing the list of modes. But when I pressed "enter" key linux kernel booted and everything was fine and continued.Autoconfiguring devices also passed.Then sound card was recognised and everything was over.And then Root# prompt appeared, then suddenly monitor started blinking again but that light on monitor kept blinking in fast intervals and nothing happened and keeps on blinking... What could be the problem?
Actually even when I installed Damn Small Linux that same problem of "You passed an undefined mode number" appeared but when I pressed "enter" it continued and everything was successfull and no problem appeared !

[Giro]

When you boot you will have a boot prompt saying press f1 for blah, Type knoppix screen=800x600 I beleve the problem is its trying to use a resolution that your monitor cant handle? Im not sure if this is it but give it a try.

[gopikrish]

Wow you are great Giro !!! That worked! I guess while installing knoppix to my HD, this problem wont occur again or should I have to do type this screen=800x600 again anywhere? And how to play any sound to test if my sound is working? But there is a speaker and I can adjust the volume at the bottom right of the screen.When I played an adventure game no sound occured.But when I rebooted knoppix, one lady said something.So any ideas are welcomed.Thanks !