You should move the router, having the wireless signal in the basement is the worst place for it, unless someone lives in the basement. If you can't move it for some reason (no ISP connection anywher else), try to run a cable from the modem up to the main house somewher and plug in the router there.
Powerline adapter would also work, you can hook up a wireless access point off the other end of that to get a stronger wireless signal into the house if you can't move the router itself.