iBook modem disconnects

[Christopher Raphael]

Hello,
The snow iBook with OS X.1.4 is disconnecting from the internet after 
about 3 minutes. Matters not whether downloading e-mail nor browsing.  
In network utility I pinged the address and got to 5:38 before it 
stopped receiving, whee! When I watch the activity in internet connect, 
it appears to send but not receive data for a minute before it times 
out (?) and disconnects.
I have tried both of my dial-up services same result.
Reinstalled OS.  nada!
Loaded X.1.5. nada!
Any suggestions?
Chris