I don't know why my WIFI is having a problem if other laptops connect to it. Should I buy a wireless extender? I think its not because of the router's range because when no one is connected to my network it reaches my room with 4 bars. But when my sister connects her laptop to the wireless network then my connection drops randomly.
Increase the number of clients to connect your internet via wireless ADSL Router or modem , I have showed example of my WIFI modem config window screen shot, hope you know to access your modem and try this.