Many of these answers are good, so I will sum up what most of them are trying to say.
1. An SSD will greatly improve system performance. By offloading information from the disk super fast, it improves overall system performance.
2. More RAM could help. 8GB is about all most will need. 16+ is for workstations and stuff like that. 4GB could use another 4GB stick.
3. Viruses. I don't know what anti-malware software you used, but for all I know it was malware in itself. Run a Windows defender full scan, and you really should get Malwarebytes.
4. Uninstall any programs you don't use. This can really help. Crowding your desktop may also do some light damage.
5. System reset. A system reset will always restore your PC to top working condition. It can really only go down from there.
Well, I hope this helps! If so, please hit the "this was helpful" button.