using timer

Hi,

  I want to stop a process which is already counting number after some time ( 2 mins).

  I have defined a timer in new form instance trigger.

  at form level defined "when timer expired"

  i have a button which starts counting number in a loop from 1 to 2000. should repeat until time expired.

 once form opened I am pressing the button which started counting numbers. But it's going infinite loop and the code in "when timer expired" not firing.

 please suggest if i am missing some thing here.

Thanks
raj