How to modify screen element in module pool

Hii...

I have developed a screen with table control..my requirement is

I have one column (i.e) check box in edit mode..after it was checked and pressed 'enter' I want to go for display mode only..how can I solve this problem..

i tried like this but this is not working..

if checkbox = 'X'.

Loop at screen.

screen-active = 0.

screen-input = 0.

modify screen.

endloop.

regards

sugu