Noticed that I do not have a CMOS jumper, probably never did. But since it was working well before anything, and turning it off (by case button), it shouldn't be playing up like this.
Most st of the checklist is good here, everything is in place and where it's meant to be, tried with extra sata power connection as well, bios switches etc.
GPU is firmly in with 8 pin power, 24 and 8 (4+4) pin also connected into motherboard firmly
Single bios mode makes it hang at code 15 indefinitely.