Welcome to the TH community, IamFaisaL!
I'd advise you to check how your secondary HDD would appear if you plug it in a different SATA port on the motherboard and also using a different SATA cable. In case this doesn't work, you should
try resetting BIOS . This would get your BIOS settings back to factory defaults, so you'd need to re-configure any manual changes you might have made already. However, it might also help you with the detection issues. If it still doesn't work, find another PC where you could plug the hard drive and check how it would get recognized there.
Hope it helps. Let me know how it goes!
SuperSoph_WD