It is either PSU or motherboard. That is if you are describing this correctly if you are meaning no signal on monitor we can put the GPU in as possibility.
It is though a sign of PSU failing if the power button does not react instantly to being pressed that is has to be held in or pressed multiple times.
Glad you mentioned the PSU and the power button, it is completely normal, no holding down required. So that rules it to motherboard if you're leading me in the right path. Thank you.