multi threading in asp.net

hello

i am using multi threading n my code...i want whent user check the checkbox..the thread starts...nd start accessing values from database nd when user uncheck the chkbox thread should suspend ..or stop

but problem is when user check the chkbox..thread starts working..fetch data from database nd then stops...
i want thread to continue look into database for if there is any nw values coming in database..what should i do....

is there any way to solve this problem...i m designing a chat application....so plz help