you initialize the value in page_load
99% you did not surround it in IsPostBack.
which means that the value is being re-initializd every time the page loads.
however, the page loads also on call backs after button submits.
you need to put this in page_load:
if(!IsPostBack)
{
//initialize nom here;
}
this will make sure nom is only initialize when page first loads, and not every time you click a button