can enyone tell me how can i made a simple boot loader to switch a video mode, and then show some string :( ?

There are thousands of such examples on google...

And recently, exactly such an example was posted to
http://groups.google.com/group/alt.os.development?hl=en

You need good search skils and very good understanding of complicated and sometimes stupid technological and hardware issues... to make an OS.

Otherwise you will become more confused... take it slow and most important take it honestly

Unless you show what you have tried and what progress you have made so far... nobody is going to write it for you...(or at least not me)