If it doesn’t work, try a full system install again. There are always reddit windows keys available for a clean install. This will delete all of your files and applications, so create a backup of any critical data before starting. If you've just installed new hardware to your system, this might...
Low disk space is usually the most common problem. If your hard disk is nearly full, your system may run slowly. Consider removing unused files and applications, or upgrading to a bigger hard drive.