With horrible pc parts price I bought this Office PC with a Asus Prime B360M-K to upgrade as a gaming pc but the chiniese GTX 1650 Low profile I bought does not boot sometimes. It gives 1 long beep and 3 short beeps gap and another beep. card fan does spin all the time.
Do you still use the optical drive? If not just leave that unplugged
The GPU (and CPU, for that matter) at full load will draw more than it does at boot. Just because disconnecting the optical drive bought enough headroom to successfully boot does not necessarily mean that the computer will be stable under load.