Try disconnecting everything from the front panel header and leave the PW wires for power button connected only to the place shown on the diagrams from my previous post. If that doesn't help leave it like that and remove the GPU and then try to power on. If that doesn't work turn off the PSU, then remove CMOS battery, wait 30 seconds and put it back again. If that doesn't work try connecting the old power supply(just connect the 24pin and 4pin to CPU) and power on.
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