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 !

You might try entering a zero (0) at the question, see how it goes.

Well I tried using Knoppix vga=normal at boot and that message "You passed an undefined mode no." didn't occur but monitor blinks fastly later.Actually when it was blinking I kept on pressing ctrl-alt-del and after sometime it returned to the dos window and there the following was written,
Starting single X-window session for user knoppix. Please stand by a few seconds while the optiman configuration is being determined.
After this system terminates, the system will automatically shut down.
Starting X11...[drm:drm_init]*Error* Cannot initialize the agpgart module
root@tty1[/]#

So this was there, I dont know whether the above was displayed before that blinking occured or during or after that blinking process.So please help what to do as I am struggling