The critical time for a new PSU is right out of the box, so it should be tested before installation. With all connections removed and the unit turned off (the "0" side of the switch), unbend a paper clip and slide one end into the green wire hole on the large motherboard connector. Slide the other end into any black wire hole on the corresponding motherboard jack, then turn the unit on. If the fan runs, install the PSU. If not, it's defective. I've wasted boocoo time installing PSU's that were DOA -- even the best brands.