Losing Internet Connection

I have a DELL 4600 with windows XP HOME edition that I’m having problems with.
I keep on losing the connection to the Internet. I have a cable modem with a cable router.
I did check to make sure it was not one of them. The modem and router are working fine. I took my laptop and hooked it up to the router and I am able to get to
The Internet with no problem .The laptop is running windows 98. If the DELL with
Windows XP sits at Idle for about an hour, it loses the Internet connection. To get it back, I have to right click on the local area connection icon by the clock and click on repair connection. Can you tell why the XP loses connection? How can I correct it?