Sounds like you have a signal coupling
problem. X10 signals have trouble going from
one phase of your home electrical system to
the other phase. Many instalations need a
coupler added to get the signals on the
other phase of the homes wiring. Also some
devices like computers and newer tvs absorbe
the x10 signals. You may want to try
selectively unpluging things and trying an
outlet that didn't work. Sometimes you can
see if you need a coupler by turning on a
220 appliance like an electric dryer and
seeing if a dead outlet then works. This is
not a 100% test but may show something.