Got an R9 270 today, was told I could run it on 450w power supply, crosschecked and that was right, as 500 is recommended, but I'm not getting any kind of POST. I've tried everything, putting old GPU back in, reseating it (It clicked when I did so so it connected properly) and yet it still doesn't work. on PSU Calculator, it says the wattage it is using is 436W with those specs.