Internal Modem Lockup on Connecting

I have a Hp Pavilion XT983, 1.4ghz Athlon,128 meg memory,, Every time I connect to the Internet with and internal modem the computer locks up. But yet I install an external modem and connect, It works fine, Can anyone offer any suggestion?? I have formated and used the recovery disk to restore windows xp home, twice, replaced the modem(new), and switched the PCI slot inwhich the modem was in and still i get the lockup…
Thanks