How to Personally diagnose a Slow Computer.

1st check for space
then check your system configuration
 The first step to fixing a slow computer is to verify that your machine is the actual source of the problem. Videos that seem to buffer forever, and websites that take ages to load, may not be your computer’s fault. iteem agent claims that many people mistakenly identify a slow system as the problem when “it’s actually not the computer, but their broadband connection.” See  below for instructions on how you can personally diagnose a slow connection.

If the problem is your PC, check whether you have plenty of free space on the hard drive holding your operating system. Windows needs room............
to create files while your system is running. If your hard drive is pushed to the limit, performance suffers. Now is the perfect time to clear some space.
If your computer’s operating system resides on an overstuffed C: drive, clearing out some space could boost OS performance.

Microsoft’s System Configuration tool is your next-best bet for tackling slow performance. Many applications launch automatically when your machine boots up, which can stretch out boot time—especially on older, slower PCs. Make a habit of trimming the startup items. Open the tool by pressing Windows-R, typing msconfig, and pressing the Enter key.

Checking the Startup Item and Manufacturer columns is the best way to figure out which potential performance-killers you can safely disable. Avoid messing with any of the services and programs that have Microsoft Corporation listed as the manufacturer. Items such as AdobeAAMUpdater, Google Update, Pando Media Booster, Spotify, and Steam Client Bootstrapper are all fair game. Regardless, err on the side of caution: If you’re not sure what the program or service does, don’t disable it.
Windows' System Configuration Tool gives you a chance to cripple projects and services that naturally begin when you boot your PC.

Once you've rolled out all your improvements, click OK and restart the PC. It ought to boot up faster and feel recognizably speedier