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.
Look up the beep codes for your motherboard in the manual (find on their website) to confirm what the beeps mean. (Good to have downloaded/bookmarked anyway)
Next/first, with the computer turned off at the PSU (but still plugged in) try removing and re-slotting the GPU (there may be a button/leaver to release it on the motherboard. There may also be a screw holding it into the case on the inside at the back). If it only sometimes doesn’t work, that indicates it’s probably just a bad connection.
I’ve a similar board. Long-short-short-short means no graphics adapter detected, and then that pause with one short beep I think means no keyboard detected.
Edit: ASUS have stopped putting the beep codes in their manuals for some reason so I don’t know where one is expected to find this information out. It was in my manual but that’s a much older model.