Reinstalling windows should be a last resort, not the first.
What is running on start-up?
Select “Start” then “Run”, then type: MSCONFIG then hit enter.
Select the Startup tab. Anything that is checked-marked executes and runs on start up. Do you need all that stuff running ? If not, uncheck it. After unchecking whatever you think needs to be unchecked, then click “Apply, then ok.
Others recommend disk cleanup and scan disk. Do it and do it now.
Run an anti-spyware and a good anti-virus.
Download malwarebytes then run it.
Always verify whatever the results of any anti-spyware\virus scan return, as they can identify things as viruses when they are not.
Also, you can set windows up to run for performance.
Select: Control Panel\System, Select: Advanced System Settings. Select “Advanced”. In the performance box select: “Settings”. Check the box for “Adjust for Best Performance” then click “Apply” then ok.
delete everything out of all you “TEMP” folders.
Do a search on C:\ for “TEMP” to find all the folders.
Restart you PC then run defrag again.
Just some easy things to do.
When in doubt, don't..ask first.
Slow computer, with not much hard disk space in use, points to running more processes than available memory can handle. It may be thrashing - meaning you are using more memory than is available. When that happens, windows, which is always prioritizing and swapping from one task/process to another, has to write ] memory to disk (called virtual memory - where you are temporarily storing what’s in memory to the hard drive) - in order to make ‘room’ in memory for loading something else to run. If it’s doing this every time it’s switching processes, your computer will take forever to do anything.
Looking in your startup folder is a good idea as was mentioned ... these are programs that automatically load whenever your computer starts - if a ton of programs are running in the background - and they may be invisible to you, that is one thing that will use all your memory.
Use Ctrl/Alt/Delete and go to the processes tab of the task manager (which comes up when you use ctrl/alt/delete). Take a screenshot and post it here.
There are processes and services running all the time on computers that aren’t what you think of as programs or exe’s.
The list will be pretty long, even for a clean computer. I would suggest taking a screenshot of that tab and posting it.
What year is the computer?
... regardless, there is too much loaded in memory, which is what would cause any action to be slow - including opening documents, switching from one program to another. You said a file search on the computer takes forever - that’s usually a process that does this when there isn’t enough memory available.
If, when it’s slow, you hear a lot of the crunching of the hard drive (as it’s reading and writing to disk), then it’s continuously swapping memory to disk - temporarily ‘putting down’ a task so that it can handle another task. Then for the next task, it has to write memory to disk to free up memory deal with the new task.
That kind of thing can be caused by having too much open at once, or too many background processes running, or it could be a virus that’s having the same effect.
Screenshot of exe’s running and processes running - both of which you can get from the ‘task manager’ using ctrl/alt/delete will show this.
Of course you can reformat the drive and reinstall windows ... but that really shouldn’t be the first resort.
I don’t using cleaning utilities on my computer, but some of the ones mentioned here are i’m sure fine.
Summary: Find out what’s hogging all your memory, and get rid of what you don’t need. (For the step of knowing what you can get rid - often you’ll recognize some things, but many processes have seemingly random names and you can’t figure out which is good stuff and which is wasteful stuff - which is why I suggest posting the screenshot of the list of your processes here)