Router help

Ok i need some help and have bought a new router and searched for hours on internet. My lil sisters computer makes the router reboot real quick and for that second i get disconnected from my games.
The router is a linksys and i had a dlink before and did the same thing. i tried re formatting her computer and almost everything can anyone guess why just her coming online would make it disconnect for like 5 10 seconds sometimes it dont and most time it does. Its very annoying. Has anyone experienced problems like this?