You may have power fluctuations causing the power to drop below intended levels. Do you have a bunch of high-draw devices plugged into the same circuit? IE a large plasma TV surround sound system, computer & monitor, etc. If all these are drawing off the same circuit and you have fluctuations in your power, it can cause all kinds of strange problems.
I would suggest getting a line conditioner (NOT a surge strip, those are completely different) that is rated to the appropriate wattage you are going to be driving behind it. Add up the total watt draw on all your gear before buying one.
Also, many of these line conditioners come with a guarantee that they will protect the devices behind up to a certain dollar amount. So IF something were to happen and the line conditioner did not function properly, they will effectively buy you a new device.
I use line conditioners professionally every day (I assist with the installation of MFP's [copy machines] onto networks) and have seen the benefit of having one.