RX 480 problems with new pc

[JK93]

Hey folks so i got a new pre built pc from overclockers but had to return it for repair, had a faulty psu, the repair form says "psu was causing system to not work with a gpu, replaced with superflower 750w psu and tested on furmark and prime95 overnight" so i've just got it back, and everything's fine now except this one issue, at first i couldn't get a signal on any gpu so used integrated graphics, then after using DDU the pc is now picking up a dedicated gpu in device manager.

i plugged in an old R9 280 after the 480 and it works fine no problems, but when i plug in the RX 480 there's no signal and also no power to the keyboard and mouse when plugged in, my specs are b450m, 3400g cpu and a superflower 750w psu. The 480 works fine, lights up and fans spinning it's not an issue with the card. The msi 480 is 8 pin/6 and 2, but the psu sata cables in the pre built pc are all 6 pin and there's no 8 pin sata slot so is it simply the psu not enough power getting to the card. The psu has 4, 6 pin sata slots whereas the cpu and motherboard does have 8 pin slots. so it's obviously just a cable issue and not enough power?

 

[JK93]

Slighgly confused as sata cables are for hard drives do you mean pcie cables for the graphics cards ,there should be some with 6 pin and 2 extra pins connected to the same cable.

Yeah the pcie cable curently connected to the pc, sorry i'm tierd and not too savvy PC wise, all i know is the problem i mentioned, the old 280 works fine whereas when i plug in the 480 with the pcie cable that came and installed with the pc, no signal, no power to keyboard or mouse. I've got a bunch of fresh pcie cables it's not an issue with the particular cable, i insert the 480 correctly, put in the 6 and 2 pin cable but no signal or power to k and m unfortunately.

 

[JK93]

Yeah no signal to monitor, no power to keyboard and mouse too. The fans spin fine, lights up fine.

Do you mean no signal to the monitor ?

Do the fans spin on the 480 ?

Try a diffrent port on the gpu.

Try the gpu in the second pcie slot.

Yeah mate fans spin perfectly it's a new gpu too, inserted correctly, the light on the motherboard is fine, tried both slots on the MB, same result, what do you mean by try a different port? I've inserted 2 different ports that are on the cable as far as i'm aware with no luck.