help me with Pmode!!!!

look at this simple programm:

mov ax,0b800H
mov es,ax
mov ah,1bh
mov al,44
mov di,666
mov es:[di],ax

as you see, it writes a single character on the screen.

But i'm need this programm to be written in protected mode....
i've tried severela tutorials, but not achive this task.
My programms usuali reset computer or hangs
Please help me!
write simple program to me sincosltd@hotmail.com
Please! and again PLEASE!!!!!