If you are using wireless "g" (i.e. 802.11g), then there are only three channels which are totally non-overlapping (i.e. don't interfere with any others). They are 1, 6 and 11. See what channels the others are using and hopefully one of those three won't be in use by the others, if so change to using that one.
I have found that wireless routers are very very unreliable and over a relatively short space of time they simply stop working properly and need replacing.