Powers up but no boot.

History: some 4-5 months ago computer would not boot unless psu was toggled off and power fully cycled then would boot as normal, otherwise everything would power up but screen remains blank, no bios splash, nothing.

As of two days ago, it does that always, regardless of being power cycled or not, and will not boot, everything still powers on.

What's been done/ruled out: psu has been upgraded and replaced, ram has been tried in all slots including using only a single stick, cmos battery has been replaced on the motherboard, issue persists whether using gpu or on-board graphics so that's not the issue.

My next guess is motherboard? I appreciate any insight or things I can try to fix.