D-Link DI-614+

I purchased two of these wireless routers w/ built in 4 port switch. I gave one to my Dad for Christmas and set it up so he could hook up my mom's computer, wired, and his (downstairs) wireless. Works great for the wireless, no complaints there. But my mom keeps complaining that every so often, her internet connection goes out, she says she'll reboot the computer and everything is fine again. She asks me, I get into her router and check all of the settings, looks fine, check her NIC, that's fine too. So I decide to hook mine up here. I only have one computer, but bought if for future use (good sale). I am not having any problems for the first couple of hours, surfing the net, getting good speeds etc. Then leave for a couple of hours, come back and no internet. Restart computer, and it's fine. It's always the wired computer. So I think that it's DHCP lease time, no that's set to 1 week, maybe I should turn off DHCP and get IP manually, nope still disconnects if I do not access internet for 1 hour or so. Any ideas as to why this is happening????