Laser printers draw a lot of current, which is also why they are generally recommended NOT to connect to a UPS, as they will overload it. They can also cause "noisy power" on the AC circuit that they are plugged into. It appears that you suffer from insufficient electrical power on that circuit, I would attempt to move the laser onto a different circuit, or get an electricial to find out what is going on, if you need a wiring upgrade, if your existing wiring has degraded/oxidized, etc. I lived in a place once, where if the microwave in the kitchen was used, the computers would reboot in the other room, if they weren't on a UPS. (Yes, the lights dimmed slightly too.)