when connect to internet computer hangs and after 15-20 minutes it get back from hang

sometimes when i connect to internet, my laptop hangs, after 15 - 20 minutes it returns from hanging and works normally(but i dont want to wait much) so sometime i hibernate my laptop for getting out the laptop from hanging or if it doesnt respond i usually shut down the laptop by pressing the power button, when shutting down its written that windows explorer doesn't responding and i click on end now button. if notthing works (shut down, hibernate) i have to shut down it improperly

i am using a dial up modem connection. i have toshiba m35x-s109 laptop with celeron m and 256 ram and have windows xp home edition.

can anyone tell me how can i solve this problem.