One of my computers will not power up. Tried a different PSU and still nothing. It was working fine last night but when I went to turn it on today, nothing. Checked all the wiring from the case and it's fine. Any idea's? One other question, will a power supply start up if it's not in a computer? Have tried just plugging 3 PSUs in and turning them on and none will turn on, one is brand new? Tried both the UPS, which has power, e.g., the monitor orange light is lit when it's plugged in as well as a power strip that has the red light lit. Do not have an extra mobo so can't try swapping. Thanks