2 Disk Drives Disappeared

Hello,
Recently I found that my disk drives - B: and Z: have disappeared.
B: used to have torrent downloads and other data, while Z mostly had media files. And data WAS important.

I have had 4 partitions, C(OS drive), K(has all kind of data), B and Z.

I'll list down recent activities which might help you in some way.

-On 9th, i.e 4 days back, I had run Auslogics Disk Defrag v3.2.1.10 and B, Z and K were lightly fragmented and defrag was done within minutes. C was getting defragged and then had to pause it cause a movie was being played and it kinda interrupted in the playback.

Later as it was taking too much of time, I stooped the process and decided to defrag it later.
Note: I had run the defrag tool, 2-3 months back.

-On 11th, i.e Thursday night, I had downloaded a bluray movie's torrent (was of 12gb). After its 100 MB sample was downloaded, viewed it and deleted the torrent from uTorrent. So the 12 GB mkv file was downloaded too, say about 20 MB of it was downloaded. Then I deleted that 12 GB mkv too, by going into B:/torrent downloads folder/movie folder.

Just before that torrent thing, I had attached my USB drive and copied some data in K drive and it seems to be intact. I am in Safe Mode and just scanned it with Malwarebytes and Avira(my current anti-virus which runs with Immunet Cloud AV) and 1227 items were detected, all in RECYCLER folder. Back then I just copied and detached the USB drive and Avira didn't detect anything in Realtime protection mode. I will attach the MalwareBytes logfile which may help you. :)

-On Friday morning(i.e yesterday) my brother was playing and tried to play some music from my B drive, and he got a message that the drive is missing.

I discovered that the B drive was missing and checked diskmgmt.msc, and it says 380 GB of space is Free.
And while i was checking for possible solutions, I found that Z drive too is missing.
Here's the diskmgmt.msc screen:


I am not sure if "System Reserved" partition did exist before this happened.

My HDD's device properties, which might help:


Its capacity is 1 TB and is about 11-12 months old.
So what could be the cause, and can I retrieve the data by myself(I think I'm a geek :P)? Or will need some professional help?
Thank You.

EDIT: Currently I am in Safe Mode and run MalwareBytes Full Scan and found nothing other than a riskware, which is Blur game's trainer which exists since 8 months.

Nvm, used this - Download Free Partition Recovery Software, Data Recovery Software, Partition Manager. and I think most of my data was recovered.
Whoops, sorry for double-post. :/

Oh wait, could someone explain me, of why this happened? I'd wish to know the reason. Thanks. :)