Just a little confusion with DI 624 c

I played Rise Of Nations(Computer games) long times ago, but when I moved to other place, the router from Netgear become Di-624, and it starts to laggy, very laggy. And the internet sometimes go slow, sometimes can't even connect. I played Rise Of Nations before it has no laggy problem, and two users with one cable modem. And here is also two users with one cable modem + DI-624 router, it starts to lag.
by the way, I have test the game when other user is not on, it still laggy as uausl, anyone can help me out? I can give any information you needed to solve it^^(The router is in my room)