loss of internet connection?

hi, i wonder if anyone can help me out.
i am on aol broadband via a netgear dg834g v3 with a phoneline connection.
my pc is connected via a lan in port 1, my son's xbox is connected via a lan in port 2, and his pc is connected via a wireless dongle.
when my son wants to use his xbox, or pc and i am not using my pc, we only turn the power on for the router and everything works fine, but if at some point, i turn on my pc,( while my son is online ) the internet connection is lost.
we then have to switch everything off, and start from scratch ( and hopefully get re connected ).
I also have a d-link dsl-2640r router, which i tried swapping with the netgear, but got the same problem.
the strange thing is that this never used to happen before and i can't understand what might have changed to cause this problem.
any help would be greatly appreciated.