I can see why you would be frustrated.
My 2 main suspects here would be either the PSU ( which you stated you already swapped out ) or the MBoard shorting out on the case.
The only way to track this down is to remove the MBoard completely from the case.
I use a rubber desk pad for this but cardboard will work fine.
With the board removed hook up only the PSU, vid card, 1 stick of RAM , mouse , keyboard and monitor and see if it will boot.
If so add one component at a time and test between each item.
Before replacing it in the case look carefully inside the case for any bent tabs, loose screws etc.
If you are missing any MBoard standoffs replace them as well.
Let us know...