Agree with both the above.
Malwarebytes is a useful tool to have on any computer and shoud be used regularly. Also go through your installed programs and remove anything you don't need, especially anything that loads at startup. then have a look in the system tray and try and disable anything that's not needed there that will also be loading at startup.
But ultimately, unless you are very good at keeping a clean system windows really requires a full reinstall about every year or so.