Cannot connect to internet

Hello,

I am using XPSP2 and a DSL modem. For some reason if I do not turn on my
modem before or at the same time as I turn on my computer, I cannot connect
to the Internet. I get no response in IE7 or MS Outlook or anything. Also,
if my computer is on and I turn off the modem and then turn it back on, then
I cannot get connected to the Internet either. The only way I can connect
is if the modem is on first or it and the computer are turned on at the same
time.

Can anyone suggest how I might fix this problem?
--
Thanks,
Bob