You might also want to ensure that you're not on the same channel with other access points in your area. Of the 11 North American channels only 3 do not overlap others (1, 6, 11). Virtually everything sold is defaulted to channel 6 and therefore instantly interferes with others.
inSSIDer: http://www.metageek.net/products/inssider/ is a good tool for determining what channel to use.