1) On startup, before opening any Windows, do Ctrl + Alt + Del to open the Task Manager. Go to the Processes tab, and look at which apps are running. If any of them look unusual, use Search to find out where they're located, and when they were last modified. Right-click -> Properties may tell you more about them. You can manually close processes in the Task Manager. You can't delete or remove an app, if it's currently running. Check the amount of CPU usage, to see if your resources are being used up by malware.
2) Go to the Control Panel -> Add or Remove Programs. See if there are installed programs,(apps), of which you are unaware or unfamiliar. Look into them, and uninstall, if necessary.
3)In My Computer, right-click your hard disk, and chose Properties -> Tools. Do the defrag analysis to see if you need to defragment.
Start with these three tasks, then try any other suggestions later in the thread.