File Upload based on checkbox

Hi ,
i am using textbox with fileupload Control(fu) and a checkbox(cb) ..
textbox(tb) is used to enter the file name.
the problem is :
i am having 3 sets as i mentioned above.
tb1 fu1 cb1
tb2 fu2 cb2
tb3 fu3 cb3

   save button

now i am uploading a file for tb1 and if i make checkbox checked for cb2 and cb3.it will get postback and the uploaded file for tb1 will disappears and it will allow  again to upload a file..

so can anybody help me to come out from this?
Thanks in advance.