At this point the next step is for a qualified electrician to address the OP's situation. he knows he has to do this so now he has to do it. it seems as if he's avoiding having an electrician come out and address this perhaps because of the money but that is most likely the problem he's having so doing anything else is just futile and a waste of time. let's eliminate the most likely culprit: the wiring or balance Etc of his home electrical. and UPS can only do so much in the long run if the electrical is really messed up in some way.
OP, please let us know what the electrician says about your situation.
OP, please let us know what the electrician says about your situation.