Go to the windows start menu. type defender. Run a scan.
Download malware-bytes free. Install. Run.
Download a program called ccleaner (make sure you pick the free version).
Install it, run. Hit 'Run Cleaner', in the bottom right corner.
Once that's done, click 'Tools' on the left hand side
Now click 'Startup'
This gives you a list of all the programs that start when your PC boots up. Some will be disabled already - the ones that run are in the darker text.
Look at this list. You don't need all this shite - Office helpers, Adobe, ITunes, stuff for your mobile phone, chat programs.... nearly everything can be disabled and will still run ok when you start the app. If you disable something and it then doesn't work, you can come back and re-enable it. Or you can give us the list and we'll pick them. Otherwise, simply Right Click as many as you feel safe disabling, them, select 'disable'.
Reboot. Try your usual apps to see if they work ok.
Go to uninstall. get rid of anything you have put on the machine that you don't need any more.
Go to Browser Plugins, repeat - but leave anything to do with video, or any add-ons that you use yourself.
Go to scheduled tasks, empty this out as much as possible (leave anything by Microsoft)
For all of the above, if you are really unsure about disbling/uninstalling something, you can google it to find out what it is. Or ask us.
Reboot.
Defrag, but not if you have an SSD.
OR
Back up your documents and do a fresh install of windows. This is so much better. You'll need to grab your windows key before you do this.
Don't do this if you have a laptop - get the documentation out and find out how to return it to manufacturer settings.