Windows98SE computer with broadband will go offline after a while

Hello,

I've got Win98SE machine and a broadband which is supposed to be always
online. The broadband modem is Terayon TA-102. At first I suspect it's
something wrong with the broadband modem and I've asked the ISP to come and
replace it. However, even after replacing the modem, my computer will still
go offline from time to time. I've tried running winipcfg to release the IP
address and update it. I can release the IP address. However, when I
update it, I get an error (I've forgotten the exact error message). And I'm
still offline after getting that error message. So every time, I have to
restart my computer to get to be able to get online again.

So what can be wrong with the whole setup? Everything used to be fine
before.

Hope someone can tell me what to check.

Thanks.

Herbert