PC suddenly became extremely slow

[DuPaCa]

As it says in the title my PC suddenly became obnoxiously slow. First, my PC was really fast, but then I started to run into some problems, but I fixed them all.
Just a couple of days ago, I started to notice that my pc was becoming really slow, I thought it was become of some processes like razer in the background, and the fact that my first HDD was getting quite full. So i moved all my games from my first hdd to my second hdd, clearing 200GB of space. I also disabled some background programs that I didnt need.
The day after I did that, I booted up my PC and I noticed how slow it had become. Something I think is worrying is that 90% of my RAM is constantly used. I already scanned my PC on malware and viruses.
Does anybody know how to speed up my PC again back to normal?

Specs: AMD FX-8320
MSI 760GA-P43 (FX) Motherboard
Club3D r9 270X GPU
CM B700 PSU
2x Seagate Barracuda HDD 500GB
CM k380 case
CM Hyper T4 CPU cooler
Windows 8.1
Belkin USB WiFi-adapter (Cable internet coming soon)

Thanks in advance

 

[ComputerSecurityGuy]

Looks like malware. Since antivirus didn't pick it up... Well, isn't it a lovely time to upgrade to Windows 10? Especially since AMD builds have seen big improvements? Just make sure to reinstall Windows 10.

 

[scout_03]

i would use ccleaner to delete all unused old stuff like cookies and temp files even old registery key not used then do a full defrag also check what is running on backgroup and stop the useless one .

 

[aldan]

and i would clean this up before i would upgrade to win10.if you do have malware all you will do is bring it with you to the new os.find out what the problem is before going off half cocked.as was said do a defrag and run a disk clean.also run some malware tools.the thing to do is download and run a scan with adwcleaner from bleeping computer.check everything it comes up with for removal.then download and scan with junkware removal tool.it will automatically get rid of anything it comes up with.lastly run a scan with malwarebytes free and quarantine anything it comes up with.do this in the order given and post the logfiles from each one.even after that it could also be a temp problem and your cpu is throttling.many variables here to look at before upgrading your os.
http://www.bleepingcomputer.com/download/adwcleaner/
http://www.bleepingcomputer.com/download/junkware-removal-tool/
https://www.malwarebytes.org/antimalware/