selection screen output (loop at screen)

Hi friends

iam working on events in reports.

with at selection-screen output iam doing screen validations(loop at screen).

my requirement is : i have checkboxes ,. if c_or = 'x' i want to dispaly 2 select-options for input .

after that start-of-selection and fieldcats are there.

but my problem was iam not getting output its only diaplaying empty list.

i had done debugging also ( on at selection-screen output) but the cursor comes out and dipslyaing empty list.

can anybody chosee the way ....

thanks in advance...

.