| Cambia:
popup_pres1 = window.open("med_pres1.asp?dato=3","Secundaria"," width=250,height=200,titlebar=no,scrollbar=no,top=
Por:
popup_pres1 = window.open("med_pres1.asp?dato=" + dato,"Secundaria"," width=250,height=200,titlebar=no,scrollbar=no,top=
Y quita la variable x |