router failure

2 days ago I replaced my modem and it works fine when cabled directly into the lady Diane's computer (XP Home) but when I plug it into the router I get no internet connection so I bought a new router this morning(netgear) again when the modem is directly into the computer I get a good connection but again when I try to go via the router (yes all the correct lights are on and the window on the task bar shows a good connection but zero internet connection. I have a headache.