help, "windows 10 suddenly unusably slow/not responding"

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So 24 hours ago my system was working. Now all the sudden it doesn't seem to. And i've no clue whats even going on. Was there some windows update I wasn't aware of that's screwing up PC's? If the hard drive was failing would windows know and tell me? Not sure where else to ask as i'm not very active on other forums right now.

Also this is horrific timing as i'm in the middle of editing final projects for college and I can't even get off my footage all the sudden.

My current video editing rig has an AMD phenom-ii 6 core (think its a thuban or something), 24gigs ram, four hard drives (two 3gig two 1gig), and a windows 10 upgrade from previous paid windows 7. All the sudden, sometime today, it just became... unusable... cpu at 1%, not much memory use, hard drive says 20% use (but no obvious tasks doing anything), and everything is so sluggish i cant even browse the menu. Rebooting the PC takes over half an hour, if it comes back up at all. I can't even get to a safe mode - auto repair failed, and it wont even give me the option to boot in safe mode. My friend who came over pulling the drive to put in a usb dock on his PC to read the files had it say something about couldn't access drives over 2tb due to some formatting not supported (everything is on the 3tb drives, mirrored, neither of which were accessible via his dock) and since i'm not an expert computer person i'm suddenly pulling my hair out.

I can think of no reason the computer should suddenly give this problem (nothing was installed, added, I dont even think I remember seeing a windows update message), none of the normal repair methods like rebooting/ auto repair/ safe mode are doing anything, and I dont even know what the next steps are when i cant even do anything.

Help? Does anyone have any suggestions and ideas of what to do or try next?