x86 Assembly : How to move code to video memory and execute the code?

Question

I’m working on simple program to change memory bank configuration of old x86 16bit PC with MASM6.

Currently, when I execute the code from the main memory it hang up. It seems that it’s because the code itself is in the main memory. When the code is executed, code itself is destroyed due to the memory configuration is changed.

Therefore I want to move the code from main memory to video memory and want to execute it from the video memory.

Please give me advices about the following codes to move the code from main memory to video memory and execute it. Executing following code still makes the system hang up.

.MODEL SMALL
.STACK 100H

.DATA
 MSG DB ' Bank Configuration is Successfully Changed',0DH,0AH,'$'

.CODE

MAIN PROC

 MOV CX,OFFSET T_HERE - OFFSET F_HERE  
 MOV SI,OFFSET F_HERE    
 MOV DI,0B800H    
 REP MOVSB    
 JMP T_HERE

F_HERE:

 MOV AX,@DATA    
 MOV AX,0B800H    
 MOV DS,AX     

 MOV DX,03872H     
 MOV AX,0DH    
 OUT DX,AX

 MOV AH9    
 LEA DX,MSG    
 INT 21H

 MOV AH,4CH    
 INT 21H

T_HERE:     

MAIN ENDP

 END MAIN