This sounds like a power issue to me. Is it a desktop computer? You could check that all the cables from the PSU are correctly plugged into the motherboard/GPU. Another thing worth trying is taking the components (RAM sticks/GPU) one by one and try turning on the computer after every part you remove, that way you can isolate the problem to a particular component. If it still wont work, then the PSU might just be fried. The easiest way to test that is to try with a different PSU, if you happen to have one of those laying around... I guess a power meter of some kind would work too, but I don't know how to go about that.
It might also be some other unexpected bullshit. I did have a similar issue recently. I swapped the PSU and everything and it STILL didn't work. Turns out there it was caused by a piece of lint in the GPU port. I took out the GPU and blew some compressed air into the port and it seems to have done the trick. I didn't even know that could happen.
If it's not a desktop computer then I don't know shit.
good luck comrade
Dark Souls 2 was the best one, I will absolutely die on this hill
king gizzard and the lizard wizard