It can't be software. So it's hardware. Since you already replaced the case, the PSU and the GPU, the next suspect is the motherboard.
But since there's nothing wrong with having a PC horizontal in stead of vertical, apart from possible temperature issues because of a changed airflow, It might be better to just accept the situation.
Please move if this isnt the right section, this is my first post here.
So 2 months ago I was cleaning out my computer with compressed air, dusted off the PSU, GPU fans, and CPU heat sync, and the case in general. I turned my pc back on and started to notice terrible fps lag inside games, making the games unplayable. After tampering with it for hours, I re-seated everything in the PC, and still no bueno. I noticed that the lag goes away when I lay the PC on it's side. Like the case is laying down. But when i turn the computer case upright, standing like it normally should be is when the FPS lag happens. So the other day I went and bought a new GPU, new PSU, and a case just because. I moved the mobo and everything into the new case, installed the new GPU and PSU. It still occurs, i can ONLY play games when my pc is on it's side, does anyone have any idea what could be the cause of this? Please help me. :/
My temps are both at 30 degrees. GPU and CPU
I7 3770k (never been OC) cpu
Evga geforce gtx 970 ssc gpu
16gb ripjaw ram
Asrock z77 extreme 4 mobo
Corsair cx750 psu
Heatsink is the standard one that comes with cpu.
I haven't noticed anything loose when i turn it over, i even tried plugging my gpu into the second pci express slot