I had similar problems in my home - modem and router in one corner of the basement and my daughter's computer in her bedroom on the opposite side of the house on the second floor. She was frequently loosing her connection; sometimes at very important times, like when she was completing university homework online.
So I purchased the "Netgear AV+ 200 Powerline Ethernet Networking Adapter Kit 100MBPS W Extra Outlet and Noise Filtering". One of the best "tech" type purchases I have ever made. With Shaw High-Speed Extreme, I average about 13 Mbps download speed in the basement at the modem and router and my daughter is always over 10 Mbps in her second floor bedroom. I'm considering purchasing another for my son's PS3 located on the main floor.