The other day, my PC shut off in the middle of using it and will not turn back on. I think it could be my PSU because it is exhibiting some of the same behaviors of what I've seen on the negative reviews for this product. However, there is still some power getting to the motherboard. The Ethernet port lights up when something is plugged in, and there is an LED lit on the board too. Even though there is still some power getting to my motherboard, could the PSU still be my problem, or is it more likely to be something else such as the motherboard, CPU, or GPU?
The power supplies I've had generally fail within 4 to 5 years. If yours is an older one you may want to replace it. When you do, get one with more power than you need and upgrade to a PSU that has multi-stage circuitry.
If you have absolutely no power, try disconnecting all add-in cards like video, sound, and USB. You might also try removing some memory cards and rotating them out. One of the most obvious and frequently overlooked is the power cord and wall receptacle and also if you are using a surge protector (especially a cheap one), try plugging your power cord directly into a wall outlet bypassing the surge protector.
You might also try disconnecting your hard drives... You won't boot up beyond the BOIS POST, but if you get any power indication reconnect the hard drive and check for the BIOS drive information. One other possibility and the easiest and cheapest to check is to replace the BIOS battery located on the motherboard. I hope this helps :)