If I could my situation would be a 100% improved.
The screen stays black, just says no signal detected and goes to standby (the monitor is fine, tested it using my 360). Already tried a new GPU (as well as the on-board GPU of the new motherboard). Nada. Since I had to get new memory along with the new motherboard I can be fairly certain that they're fine. Well, it would be very unlikely for them to be broken out of the box.
If I hadn't sold my old CPU I could have easily dropped it in to see if it POSTs, but alas... So now I can flip a coin on whether it's the PSU not giving out enough juice (fans spin and LED are on) or the CPU. I can't imagine a CPU just dying from one moment to the other, but I guess it's not impossible. That said I really hope it's the PSU, because I really don't want to get a new CPU... I guess I could get one used, but that's a gamble I'm not willing to take at this point.