Was it always this slow? Laptop or desktop? I assume that you are running an up-to-date anti-virus. What part of the computer is slow? Do you mean it takes forever to boot, too long to surf the web or is just generally slow? There are many possibilities. These are the most common causes of a slow computer and their solutions.
1. Do you have enough hard drive space?
Press Win key-E, and click on This PC, you will see a thermometer gauge under the C drive. You can also right-click on the C drive and select Properties for more information. At least 10% (better 20%) of your hard drive should be unused. If lack of free space is a problem, you have a choice between eliminating unwanted programs or files or installing a larger hard drive. Windows needs free space to function properly. This one problem alone will slow a computer to a crawl. You can easily clone (not copy) your existing hard drive onto a new and larger HD using the free version of Clonezilla or Macrium Reflect Free.
2. What is in the Start Up group?
Many programs install themselves in the start up group enabling them to load faster at the expense of constantly using computer memory and CPU resources. CCleaner, Tools, Startup will tell you what is running and also gives you the chance to right-click on the program and select disable, which does not uninstall the program but prevents it from loading every time you start the computer. You will still be able to run this program any time that you want. If you encounter a file that you are unfamiliar with, and you will, Google it to see what others say about it and if it is safe to disable.
3. Do you have enough RAM? If you have at least 8 gig, this is probably not your problem.
Right click on Computer or This PC on the Desktop and select Properties. Memory is cheap and easy to install, even on a laptop. Go to www.crucial.com and have it scan your computer to see exactly what memory your PC uses and to see how much it would cost to upgrade. (If your video card does not have adequate on-board video RAM, Windows will use system RAM for this purpose which reduces the amount available for Windows and other applications.)
4. Have you run the free versions of both Malwarebytes and CCleaner recently?
These will clean out a lot of crap and malware on your computer and free up hard drive space. Also, run Belarc Advisor to get a list of exactly what hardware and software is on your computer. Print it and save it since it records the product keys necessary to reinstall some of the software if this ever becomes necessary.
5. If IE or Firefox is very slow opening pages, go to Help and select "Start without add-ons" and see if this speeds things up. If it does, go to Tools, Manage Add-ons and disable all add-ons and enable them one at a time until you find which ones are slowing down the browser. Also, uninstall unused search engines and other toolbars. Simply not using them is not enough.
If you are not seeing the Menu bar at the top of the Firefox screen press the Alt key. To make this change permanent, go to View, Toolbars and click on Menu Bar.
What Not To Do:
Don't use anything called an optimizer or registry editor except the one in CCleaner. Especially avoid any program that finds thousands of "errors" on your hard drive that you can only remove by buying their software. Manual defragging is not necessary on a modern hard drive- Win 7 and newer do this automatically.
first check your hard drive if hard drive is working good or if never spaces hard then delete some data then upgrade your ram
What OS? What version?
What are the specs of your computer?
Upgrade the RAM, perhaps?