hard drive data recovery

I have a 2TB WD Element HDD. Last week I needed to take data from the HDD to a pen drive, and I used my laptop. Firstly, I quick format the pen drive (I'm 95% sure that I formatted the right pen drive disc). Just in a couple of seconds, I noticed my HDD has 1.81TB of free space. I was confused...

I recently replaced my motherboard, GPU, and CPU. However, at some point during the move, my secondary drive became Unallocated according to Windows Disk Management (pic) and now I cannot access it: The drive has important stuff on it (I know I know, I'm a fool for not having more recent...