Hmm, ok. If you think your A/C is causing the issue it could be a couple of reasons.
a) Voltage Drop. If your A/C is on it's own circuit and you have a good feed to the house, this shouldn't be an issue. If it's an old house with an old fuse panel, then this might be causing some issues. You might need an electrician to check it out. Try plugging a lamp with an Incandescent bulb (LED won't be ideal) into the same socket the PC or Monitor is connected to. Watch the lamp to see if the light dims when the A/C kicks in. If it does, you have a voltage drop issue. The power drop might be causing the PC power supply to go wonky on one of the rails.
b) RF Interference. I can't see this being your problem, but when I worked at the phone company as a tech we had an issue on a particular city block where anytime an electric street car went by, all our customer modems on that block would disconnect. The sparks from the overhead cable was causing RF interference that would knock out service to everyone from our node.