I am currently trying to boot an Intel D915GAG motherboard fed by a Corsair HX450W. This PSU has two 4-pin processor power supply connectors available. I tried booting with either one of these plugged into the Pentium 4 power supply connector without success. Then, I used a Molex -> P4 adapter to supply juice to the CPU and I got the motherboard to boot fine. (The RAM stick I use is fine, and the only devices connected to the motherboard are a monitor, a PS/2 keyboard and a front panel power switch.)
However, I read somewhere that the 4-pin connectors may be inverted, either on the motherboard or on the PSU itself. Since supplying power to the CPU via the Molex -> P4 worked on two motherboards (this Intel one and a MSI), it is most likely that the inversion be on the PSU. (Or that the two (brand new) PSU's 4-pin connectors are dead.)
So, my question is : what happens if I invert one of the PSU's 4-pin CPU connector, so that the two ground and +12V lines are swapped ? Will it fry the motherboard, or damage the PSU ?