Before I realized how simple it was to build, i bought a premade desktop from HP, HP Pavilion Elite e9180f Desktop PC Product Specifications HP Pavilion Elite e9180f Desktop PC - HP Customer Care (United States - English)
Since then i have moved it to a new case and added a new hdd, at which point it was working fine.
My issue came when i sought to upgrade to a new graphics card, so before doing so i bought a new PSU. Initially i bought a Corsair HX850, and after trying everything i could think of, the same problem would happen: Case + CPU fans spin, LEDs light up, but the machine doesn't POST and no signal is output to the monitor. When i went back to the old PSU, everything worked just fine. After a while of muddling around with this i decided the PSU must be defective so i returned it and bought a Corsair TX650 (At this point i realized i probably wouldn't be doing SLI in the near future, hence the downgrade).
However, to my surprise, the same exact thing happens, and reverting to the original PSU returns working order to everything, so at this point I am certain it isn't any sort of PSU defect, but rather an issue with my machine, although i cannot imagine what that might be.
If anyone has any ideas, i'd appreciate the help.