Question I think my pc is possessed and i need help

[Wombo]

Ok so basically i have this troubling issue with a pc I built where sometimes when I turn on the power supply my pc will automatically turn itself on. I tried different variations of things such as unplugging my computer and waiting like an hour, disconnecting the power button, etc. No matter what, as soon as I turn on my PS U, my pc powers up. That normally wouldn't be a problem except when this occurs the only thing that gets power is my (as far as I can tell) my PSU, mobo, and ram. GPU, fans, and everything else has no power. Also when this occurs i can't go to bios or anything because my monitor thinks my pc is still off. This happend once before but than magically fixed it's self. If u guys need specs ive got an MSI z270 m7 mobo, Intel i5 7600k, 16gs ram, gtx 1070, and PS U is a 750 watt thermaltake RGB PSU(Idk the exact model). Edit: I don't think lack of a power is th problem but it could be PS U related. Thermals are good and I can't really think of anything that would cause this.

I fixed it... The 24 pin cable was loose and wasnt connected all the way to the GPU.

 

[Math Geek]

so if you turn the psu on and then shut it down while leaving the psu on, what happens? i've got a thought but need a touch more info like this to help see if i'm on the right track or not.

does it work normal now like it should? you can hold the power button down to force the shutdown once it starts itself up.

 

[DSzymborski]

The exact model of PSU is pretty important; the Toughpower's tend to be good, the various Smart series...well...not so much. Is there any way you can track down the PSU? If it's a Smart, getting another PSU to test, from a store from which you can make a return, would be a good idea to rule it out.