Weird computer problem

[Sleestak]

Can someone help me figure out what is wrong with my computer?

I just built a new computer, Asus p5n-e with an e6600. I run windows XP and have a cable modem. I can play all night, or surf the web. but, if I take a break for more than like an hour, with no Internet activity, I will have to reboot the computer (but not the modem) to be able to use the Internet again.

Has anyone ever heard of a problem like this, or any way to fix it? Ive never had this problem before. I have all the latest MS updates and everything. I also have the built-in firewall turned off.

I would sure appreciate some help here.
Slee