It could be a few things and I don't think your PSU would stop you being able to get into windows, is the 24 pin power connector in correctly?
Does it get into windows? if not then it could be a hardware problem.
If it gets into windows then it could be worth trying to reinstall windows, if it's not getting into windows try booting up with another hard drive with windows on it before you reinstall to check if it's needed,
Did you check for bent pins?
I am guessing you're using an Intel CPU because if you had bent pins on an amd cpu it wouldn't fit in the socket, take a magnifying glass and have a look in the socket, if you find you have bent pins it can be very tricky to fix without damaging other pins around the bent one, try using a pin / tweezers to bend it into a position were it will make contact, if it was bent up out of the socket then it should still be making contact so this will only really apply if the pin has been pushed to the side or down into the socket.
Check all your front panel connectors for your power switch, reset switch and front panel jazz is all plugged in correctly, if you're trying to boot your pc and the power switch is plugged into the reset switch pin or something along them lines then that could be causing these issues also.
Also, make sure your motherboard is clear from things that could be causing it to short, check all the capacitors and chips to make sure there is no manufacturing errors.
If none of the above work, try taking it all apart and putting it back together again to make sure everything is in correctly.
If that doesn't work test your hardware on another PC if it all works then the problem is your mobo.