modify screen

hi guru's,

i have select-options like this.

cno for kna1-kunnr modif id abc,

sno for vbak-vbeln modif id bcd,

date for vbak-erdat modif id cde,

sarea for vbak-vkgrp modif id def,

mete for vbap-matnr modif id efg.

what i want is after entering input values in cno only remaining options will be enabled. otherwise these will be in disable mode.

help me.

thanks in advance.