Disk Defragmenter, which is in the same folder as Scandisk, puts everything back together. The process can take an hour or more, and you can't use your PC while it's running. Then use the Disk Cleanup utility that gets rid of unnecessary temporary files. Once you've done these three tasks, reboot your machine and see if things are better. If not, there are still a few more tricks to try.
Programs running in the background can be a big robber of system performance.
There is a chance you've installed software at some point that runs automatically every time Windows starts. Finally, it's always a good idea to make sure that your operating system and software are up to date. Shortly after signing the requisite nondisclosure agreement, I was led to a secret laboratory. My boss undid the two locks on the front door, disarmed the security system and escorted me into a crowded and untidy room. On the table was a disassembled computer that didn't look at all familiar to me.