Internet connection

Lately, we got a new Dell computer with Windows xp
professional operating system. We use the AT&T cable
modem. I have disabled the Firewall option.

I can start up the computer and get online and then
I check my email but not long after that I lose the
internet all together and also have lost it even if I
the computer is inactive for a while. So, I would like to
know what I can do to, to not lose the internet connection
on and off? Could anyone advise me if there is some other
setting which prevents me from getting kicked off.

Thanks,

Cynthia