I reinstalled Windows 10 on my desktop computer. I have two hard drives in my computer. Windows was re-installed in my c drive where it has always lived. But now, I can no longer access my d drive.this sounds to me during install the operating system was installed on C:\ and 99% of the time the image file is run from the D:\ drive. If this is the case all you had to do was give the old D:\ drive the letter recognition, it's often removed during installation.
It is very likely you have setup Bit-locker or other disk encryption for your D: drive when you started to use this computer. So, when you reinstall the OS, the data are gone.