Why do I keep losing internet connection?

My internet connection was fine, but after my sister got her macbook (I mean an hour after she started it up) we had internet connection issues. After a short time (half an hour all the way up to 3 or 4 hours) every single computer and my xbox says the internet connection is lost or unidentifyable. At this point, we restart the router and it works, sometimes for a day, sometimes for 30 minutes before losing the connection. All the connections are wired except the macbook, and ports are properly forwaded for the xbox and the PCs. Router model is a Netgear WGR614 v3.

Help! this is annoying. I will give additional info if asked. (This is all the base info I can think of right now)