Blynch, the popups do not have anything to do with the wiring in your house. That is your computers problem.
Now as far as the wiring and not knowing anything about your house or what the electrician actually did, what did he do?
He should have made sure the polarity was correct, that is just basic knowledge.
I have never worked with UPS's before, but was the red light on before he did any work? The manual would tell you if it needs to be grounded.
Have you checked all and I mean all outlets that are on the same breaker/fuse that your computer is plugged into? I have seen outlets in the basement that were on the same branch as an outlet on the second floor. There might be something plugged into an outlet on the same branch as your computer that is interfering with your monitor.
I would take your monitor to a friends house and try it to make sure that is not your problem. Then find a competent electrician to correct your wiring problems.
I live in the US, and I do not have any knowledge about wiring in any other country, so I hope this will be of some help.