Int 33 00 

Mouse Interrupt 33 Function 00h Initilizes or mouse ininialization, which initilizes the mouse and in this process
any previous mouse pointer is hidden. 

mov ax,0000
int 33

returns : 

AX = FFFFH on Suceess 
BX = Number of Mouse Buttons

if not successful 
AX=0 on Failure


mov ax, 0
int 33h