Asus system will not stay connected to the...

My son has a brand new computer set up with an Asus mother board with an onboard cable connection. He is running XP on the computer. His computer has ASUS M4A78T-E AMD 790GX Socket AM3 Motherboard
AMD Phenom II X4 955 Black Edition AM3 CPU
4GB OCZ Fatal1ty PC10666 DDR3 1333MHz Memory
Hitachi Deskstar 7K1000.B Hard Drive
Ultra M923 Full Tower ATX Case
Ultra LSP750 750-Watt Power Supply
integrated Radeon graphics plus VGA, DVI, and HDMI ports The Asus socket AM3 mobo features Dual Core Center, 790GX and SB750 chipsets. After he loaded a fresh copy of XP he went online to add updates and found that he can only stay connected for a few minutes before the computer disconnects from the internet. He can connect again, but only after resetting the connection, or rebooting the system, but after connecting again the problem returns. My son tried everything he could think of to get the computer to stay connected and we even called the cable company. They even tried rebooting his system from their end. Nothing we have tried so far has changed what has been happening. I spent a while on my computer trying to find an answer online, but the only thing I came up with was 3 other instances of the exact same thing happening in the exact same way and oddly they all had Asus motherboards. My son had even thought that it might be that the computer was not not able to run XP, but one of the other examples I found of this happening just 3 weeks ago and a very simular mother board had the same thing happen running Vista and thought that maybe their network could not handle the Vista. Even the Geek squad got involved in that one, and they could not find an solution after trying even another brand new Asus computer and having the same thing happen again, and they ended up swapping the mans computer out for a Dell and the problem stopped. My son really loves the computer and its specs and if it was not for this particular problem would be happy as a ****. What can you suggest?