My D drive is a seprerate hard drive and shows on my bios and device manager but not on my computer or windows explorer

Sometimes you have to assign it a drive letter. Right click on My Computer, click on Manage, then click on Disk Management and you see the drives. Right click on the drive in question with the blue bar over the long rectangle box. You then have the option to change the drive letter, like to F or G. Then restart the computer and it should now show up. I have often seen D get auto assigned but not get recognized. Not really sure why.