Welcome to Tom's Hardware, kamran292!
It would be really helpful if you share some more details about your system's configuration. I'd suggest you start by re-seating the connections to the HDDs and
make sure you have them properly connected. Another thing you should try is using a different SATA cable and plugging the HDD to a different SATA port on the motherboard. Just make sure you have those ports enabled in the BIOS settings.
If you are upgrading your primary/booting HDD, make sure you have the secondary drive unplugged from the mobo. Otherwise, you are bound to encounter an OS confusion that will cause some booting issues as well.
Keep me posted with the troubleshooting & good luck!
SuperSoph_WD