Turn your system on.
Press the key on your keyboard to enter the bios.
If the hard drive is connected to the system correctly Thomas in regards to power to the drive having been connected and the Sata data cable from the drive to a Sata data port of the motherboard.
The hard disk drive will show in the bios.
It will list the brand name for the hard drive, and also the storage capacity of the drive.
If you can see that in the bios then the drive is working.
If the drive is not see, or reported in the bios you will have to open up the side of the system case and check that the second drive has power connected to it from the power supply unit of your system.
And that there is a Sata cable connected to the drive, and a Sata port on your motherboard.
The reason why you cannot see the drive when windows os is loaded on your computer, but the drive is seen in the bios, and reported as detected.
Is, or will be because the drive in question has not been formatted.
If the drive does not show when you click on my computer of windows 10 once it has loaded.
Then you will need to format the drive in question.
To format the drive Thomas.
Click on the start button of windows 10.
In the search box type: disk man.
From the search results box to the left.
Left double click on: Create and format hard disk partitions.
A new window will open.
In the new window you should see a list of connected hard drives to your system.
You will see the SSD drive listed, and the storage capacity it can hold in size, and the disk number
If you see another hard drive listed with a different disk number, check what it says about the storage size for example 1Tb.
Right click on the main window where the hard drive is listed.
From the pull down menu that will appear as a list select format.
Choose the type of formatting NTFS, or GPT for the file system.
Tick the quick format check box and click ok.
Once the drive has finished formatting.
Close the open window.
And then click on my computer of windows 10 again.
You should see the other drive now listed as drive D:
If your SSD drive is listed as C: