how to make file upload works properly

I am using file upload with post back trigger but when I attach file first time it is not accept unless attached again in the second time. In addition, without post back trigger it woks but uploading the whole page that why I tried to use trigger because without it the upload button stopped

Please help

protected void Upload(object sender, EventArgs e)
{
if (FileUpload1.HasFile && ddlSelect.Text == "Document")
{
Code for Uploading file code
.
.
.
}
else
if (FileUpload2.HasFile && ddlSelect.Text == "Video")
{
Code for Uploading video file
.
.
.
}
else
// {
// for both
if(FileUpload1.HasFile && FileUpload2.HasFile && ddlSelect.Text == "Both")
.
.
.
.
{
}
asp code for trigger
"btnUpload" />