Since you had this PC, just what are your uses for it. We have no clue in the way your PC is used. It's looking like if your 1st boot drive is SSD and the 2nd drive being 1Tb has it been set to "used as storage or data drive"? I ask, because if you accept the default setting of many various s/w installs or don't pay attention, it will default to your 1st drive, the SSD. It will fill-up and basically become slower over time. If you do much audio or video editing of play which in turn stores much of that data, the SSD is getting filled too easily. The 1Tb may not being used, but again I don't know your day to day operations of the PC. If you at least check the amount of space being used by each drive and the folders/directories used you get an idea of what the status of storage. I exclude any h/w fault for now. While, you seem to be working on any malware of infection side of things, please do check those scans. One good pgm. to do all this and it will take some time is the use of "HitmanPro/64-bit version" it will load and update itself and in general does a very intensive scan outside of a typical normal boot, though it may to scan several times to be clean. Once, HitmanPro is OKs the PC, then you can proceed to other aspects of what your problem maybe.
I get the feeling, if it worked well 1 day and then didn't the next, JUST recall what you may have done prior to its downfall. If recent s/w install, remove them or any freebie s/w, un-install or delete them. Don't trust any new s/w if that's the case. Alas, if you did install something, and connected to the WWW you compound the problem as it "nestles" into your PC to wreak havoc.