It is probably because it has a format windows doesn't recognize, i had the same problem so my advise is to go to the bios of your system en look if it pops up there. if it doesn't pop up there go to your settings then click on system then on info than system info until you get to a list that shows evrthing connected to your pc (you should also see your video card) if you see the thing there but it still isn't showing up on your storage it probably has the wrong format. You can easily fix this by using programs like minitool partition wizard free, you just have to download that and change the format of the HDD or SSD if you dont even see the hardisc on the bios of your motherbord or on the list in windows it could be that you either don't have enough power, used the wrong cables or it's broken.

Sorry for all the grammar mistakes, i hope this helped you