it says i’m connected but i can’t use the internet

I need your help! I’m not computer literate at all… so detailed responses would be great.
We have a wireless internet connection(WPA) set up, and it has always worked before. one of the people living here just hooked their laptop onto the network.. and ever since she hooked her laptop on, it wouldn’t let me be on. it says i’m connected to the network with excellent strength but when i try to use a browser it won’t work. the other laptop in the house does work, but mine doesn’t ever since that one was hooked up. there is also a desktop that is connected through an ethernet cord and that works fine too.
thanks!