Microwave ovens, cordless phones, and other electronic devices can create interference. My suggestion would be, if possible, run a cable from the router to the other room, and add an access point. If you can't run the wire, you can try something like a power line adapter, then connect an access point.
It could also be that you need to change the wireless channel(s) used on the router. What is the make/model of the router - and are you connecting wireless B, G or N? If wireless N - which band are you using?