I currently own a laptop and an xbox. My two sisters both own separate laptops and we have a main household computer. Our connection is still really fast with all these, however when my older sister connects her laptop to our modem (a netgear DGN2000) everyone except the main computer disconnects. It is really annoying when im talking to someone or playing on xbox live. We have tried many different "solutions" to problems similar to this on forums but none have worked. Please help :( Its 100% her laptop because it only happens when her laptop is on for like 2 minutes.

There are two ways for a computer to connect to a wireless network: 1) dynamic (dhcp) - the router assigns a "temporary" IP address to a specific machine that is connecting to the network, or 2) static, where the computer is configured to use a specific address when connecting to the network. This is often the cause of the types of problems you are expreiencing. You need to verify that your sister's computer is using DHCP addressing instead of static addressing. If not, then go to the computer's TCP/IP settings and change it.

commented: Well said +11