You said at first you two live in the same house, then said its different houses.
If you both live in the same house and only ONE can get on, have that person set a static IP address.
If you are in different houses, reset the router completely using the back of it with a paperclip
If the router is not accessible, lets get in that bitch via the browser this may take some know-how about your router / ip addresses but normally its 192.168.1.1 in the browser

Now to get to this page it is a little advanced if you don't know what you're doing...
Once your in your router's configuration click on admin > management (will differ from your router just use some common sense) then change the default password to what ever you want it'll prompt you to login again
login again
once you do that set it to remote management mode on port 8080
now type your ip address in the URL with :8080 after it
then go back to admin tab go to factory defaults and click yes > save settings
your password will be back to default.
Yes we did have to do all that just to manually restart the router. If you don't understand any of this lmk
Edit: When you turn on remote management make sure to turn it off when you're done, it should reset with factory reset but if it doesn't turn it off.
This post was edited by Dj16921 on Jul 18 2011 09:04am